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Sample records for mg50 ni50 amorphous

  1. Bulk ordering and surface segregation in Ni50Pt50

    NASA Astrophysics Data System (ADS)

    Pourovskii, L. V.; Ruban, A. V.; Abrikosov, I. A.; Vekilov, Y. Kh.; Johansson, B.

    2001-07-01

    Interatomic interactions obtained from the effective screened generalized-perturbation method have been applied in Monte Carlo simulations to derive the bulk and surface-alloy configurations for Ni50Pt50. The calculated order-disorder transition temperature and short-range order parameters in the bulk compare well with experimental data. The surface-alloy compositions for the (111) and (110) facets above the ordering transition temperature are also found to be in a good agreement with experiments. It is demonstrated that the segregation profile at the (110) surface of NiPt is mainly caused by the unusually strong segregation of Pt into the second layer and the interlayer ordering due to large chemical nearest-neighbor interactions.

  2. Microstructure and Properties of HVOF-Sprayed Ni-50Cr Coatings

    SciTech Connect

    Joel A. Simpson; Terry C. Totemeier; Richard N. Wright

    2006-06-01

    Thermal spray coatings represent a potential cost-effective means of protecting structural components in advanced fossil energy systems. Previous work at the INL has focused on relationships between thermal spray processing conditions, structure, and properties in alumina- and silica-forming coatings, namely Fe3Al, FeAl, and Mo-Si-B alloys. This paper describes the preparation and characterization of chromia-forming Ni-50%Cr coatings, an alloy similar to the INCOCLAD 671 cladding, which has shown excellent performance in the Niles Plant service tests. The structure and properties of Ni-50Cr coatings are similar to other HVOF-sprayed metallic coatings: a typical lamellar microstructure is observed with essentially no porosity and little oxide. The microhardness and compressive residual stress both increase with increased spray particle velocity. Corrosion tests were performed on a variety of free-standing coatings (removed from the substrate, wrought Fe3Al alloy, and Grade 91 steel in a simulated coal combustion gas (N2-10%CO-5%CO2-2%H2O-0.12%H2S) and gas-slag environments (same gas, with iron sulfide powder in contact with the coating surface). The coatings tested included Fe3Al, FeAl, and Ni-50Cr alloys sprayed at different velocities. In these tests the iron aluminides in wrought and coating form showed the best performance, with Ni-50Cr coatings slightly worse; the Grade 91 steel was severely attacked.

  3. Atomic scale understanding of magnetic properties in Ni50Fe35Co15

    NASA Astrophysics Data System (ADS)

    Herojit Singh, L.; Govindaraj, R.; Ravishankar, C.; Rajagopalan, S.; Amarendra, G.

    2016-02-01

    Mössbauer spectroscopic studies have been carried out at different temperatures across ferromagnetic to paramagnetic transition in Ni50Fe35Co15 and the evolution of hyperfine parameters such as centre shift and magnetic hyperfine fields with temperature has been studied. Mössbauer spectrum obtained at 300 K in Ni50Fe35Co15 exhibiting fcc crystal structure is a six line pattern with the mean value of the hyperfine field close to 33 Tesla. Ferromagnetic to paramagnetic transition has been observed to occur in this system around 895 K matching with that of magnetization results. Debye temperature of this nickel rich alloy is deduced to be around 470 K matching with that of Ni. Effect of prolonged annealing at 750 K on the magnetic property is also investigated with respect to the thermal stability of the alloy .

  4. Laser Cladding of Ni50Cr: A Parametric and Dilution Study

    NASA Astrophysics Data System (ADS)

    Song, B.; Hussain, T.; Voisey, K. T.

    The increasing use of biomass as a fuel is leading to higher fireside corrosion of the heat exchangers in boilers due to the high chlorine and alkali metal content in the fuel. Laser cladding of Ni50Cr is a promising technique to enhance fireside corrosion resistance of boiler tubes from this aggressive environment. A parametric study is carried out on the blown powder based laser cladding of Ni50Cr on 304 stainless steel. Successful deposits were generated and the effects of the various process parameters on clad geometry and dilution are reported. The various commonly used techniques for determination of clad dilution are compared and some guidelines for their use are suggested.

  5. Magnetism and magnetocaloric effects in Ni50Mn35-xCoxIn15 Heusler alloys

    NASA Astrophysics Data System (ADS)

    Pathak, Arjun K.; Dubenko, Igor; Pueblo, Christopher; Stadler, Shane; Ali, Naushad

    2010-05-01

    The effects of the partial substitution of Mn by Co on the magnetic, magnetoelastic, and magnetocaloric properties of Ni50Mn35In15 Heusler alloys were studied using x-ray diffraction, temperature and field dependences of the magnetization [M(T,H)], and strain gauge techniques. It was observed that the presence of ≈3% Co atoms in Mn sites strongly affected the magnetic and magnetoelastic behaviors of Ni50Mn35In15. At H=5 T, a maximum magnetoelastic strain of ≈0.6% was observed for Ni50Mn35In15. It was found that Co substituted into the Mn position does not affect the ΔSM in the vicinity of the second order transitions (SOTs), however ΔSM near the first order transitions (FOTs) it slightly decreases. The net refrigeration capacities in the vicinity of both the FOT and SOT were found to significantly increase by introducing Co into Mn sites. The net refrigeration capacity in the vicinity of the FOT and SOT was found to be 167 J/kg (T=277-293 K) and 229 J/kg (T=305-354 K), respectively, at a magnetizing field of 5 T. These values of the magnetocaloric parameters are comparable to that of the largest values reported for metallic magnets near room temperature.

  6. Electric field modulation of magnetic anisotropy and microwave absorption properties in Fe50Ni50/Teflon composite films

    NASA Astrophysics Data System (ADS)

    Xia, Zhenjun; He, Jun; Ou, Xiulong; Wang, Yu; He, Shuli; Zhao, Dongliang; Yu, Guanghua

    2016-05-01

    Fe50Ni50 nanoparticle films with the size about 6 nm were deposited by a high energetic cluster deposition source. An electric field of about 0 - 40 kV was applied on the sample platform when the films were prepared. The field assisted deposition technique can dramatically induce in-plane magnetic anisotropy. To probe the microwave absorption properties, the Fe50Ni50 nanoparticles were deliberately deposited on the dielectric Teflon sheet. Then the laminated Fe50Ni50/Teflon composites were used to do reflection loss scan. The results prove that the application of electric field is an effective avenue to improve the GHz microwave absorption performance of our magnetic nanoparticles films expressed by the movement of reflection loss peak to high GHz region for the composites.

  7. Magnetic properties of Ni50Mn34.8In15.2 probed by Mössbauer spectroscopy

    NASA Astrophysics Data System (ADS)

    Khovaylo, V. V.; Kanomata, T.; Tanaka, T.; Nakashima, M.; Amako, Y.; Kainuma, R.; Umetsu, R. Y.; Morito, H.; Miki, H.

    2009-10-01

    Structural and magnetic properties of a Ni50Mn34.8In15.2 ferromagnetic shape memory alloy doped by F57e at the Mn sites have been studied by x-ray diffraction, Mössbauer spectroscopy and superconducting quantum interference device magnetometry. Obtained experimental results have disclosed unique magnetostructural transition from a high-temperature ferromagnetic austenitic phase to a low-temperature paramagnetic martensitic phase at Mf=290K . Complex magnetic ordering which can be classified as a cluster glass state is formed in Ni50Mn34.3F57e0.5In15.2 on further cooling below TCM=162K . The abnormal magnetostructural transition observed in Ni50Mn34.3F57e0.5In15.2 is suggested to originate from the weakening of exchange interactions due to an abrupt change in Mn-Mn interatomic distances occurring upon the martensitic transformation.

  8. Selective leaching and surface properties of Ti50Ni50-xCux (x = 0-20 at.%) shape memory alloys for biomedical applications

    NASA Astrophysics Data System (ADS)

    Chang, Shih-Hang; Chiu, Wei-Chen

    2015-01-01

    This study investigated the selective leaching and surface characteristics of Ti50Ni50 and Ti50Ni50-xCux (x = 5, 10, and 20) shape memory alloys (SMAs) by employing inductively coupled plasma mass spectrometry, electrochemical tests, and X-ray photoelectron spectroscopy. The experimental results revealed that Ti50Ni50-xCux SMAs exhibited corrosion-resistance properties that were more favorable than those of Ti50Ni50 SMAs, whereas the concentrations of the Ni and Cu ions selectively leached from Ti50Ni50-xCux SMAs were considerably higher than those of Ni and Cu ions selectively leached from Ti50Ni50 SMAs. Ti50Ni50-xCux SMAs exhibited higher selective leaching rates of Ni and Cu ions than those of Ti50Ni50 SMAs, because the NiO and Cu2O oxides that formed on the surface caused a deterioration of the uniformity and protection of the passive TiO2 films. Although Ti50Ni50-xCux SMAs exhibited unique properties that are superior to those of TiNi binary SMAs in particular biomedical applications, appropriate surface modifications are necessary to avoid the risk of toxicity caused by the released Ni and Cu ions.

  9. Magnetic field dependence of electrical resistivity and thermopower in Ni50Mn37Sn13 ribbons

    NASA Astrophysics Data System (ADS)

    Maheswar Repaka, D. V.; Chen, X.; Ramanujan, R. V.; Mahendiran, R.

    2015-09-01

    We report magnetization, magnetoresistance (MR) and magnetothermopower (MTEP) of melt spun Ni50Mn37Sn13 ribbons which exhibit an austentite to martensite phase transition at a temperature (TM) ≈ 294 K. Upon cooling from 400 K, dc-resistivity and thermopower show abrupt changes at TM, indicating a change in the electronic density of states. The thermopower is negative from 400 K down to 10 K. Application of a magnetic field of μ0H = 5 T decreases TM by 5 K and induces large negative MR (-23%) but positive MTEP (9%) near TM. While the MR is appreciable from TM down to 10 K, MTEP is significant only below 60 K (MR = -2.5% and MTEP = +300% at 10 K). The magnetic field dependence of resistivity and thermopower show either reversible or irreversible behavior near TM, depending on whether the sample is zero-field cooled or field-cooled, which indicates that the electronic band structure near TM is magnetic history dependent.

  10. Investigation of the Deformation Activation Volume of an Ultrafinegrained Ti50Ni50 Alloy

    NASA Astrophysics Data System (ADS)

    Gunderov, D. V.; Churakova, A. A.; Lukianov, A. V.; Prokofiev, E. A.; Prokoshkin, S. D.; Kreizberg, A. Yu.; Raab, G. I.; Sabirov, I. N.

    2015-10-01

    The mechanical properties, strain rate sensitivity (m) and deformation activation volume (ΔV) are investigated at the experimental temperatures from 20 to 400°C in a Ti50Ni50 alloy in a coarse-grained (CG) state with the austenite grain size D = 200 μm and in an ultrafine-grained (UFG) state with D = 700 μm following an ECAP treatment. It is observed that this treatment improves the yield strength of the alloy compared to its CG-state. The strain rate sensitivity, m, is found to be by a factor of 1.5-2 higher than that of CG-specimens; it increases with the temperature in both states of the material. As the temperature of the material in tension increases up to Т = 150-250°C, parameter ΔV increases to its maximum and with a further growth of the experimental temperature to 400°C, parameter ΔV decreases. The deformation activation volume of the alloy in the UFG-state is by a factor of 2-4 larger than that in the CG-state for the same experimental temperatures.

  11. The martensitic transformation and magnetic properties in Ni50- x Fe x Mn32Al18 ferromagnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Xuan, H. C.; Zhang, Y. Q.; Li, H.; Han, P. D.; Wang, D. H.; Du, Y. W.

    2015-05-01

    The martensitic transformation (MT) and magnetic properties have been investigated in a series of Ni50- x Fe x Mn32Al18 ferromagnetic shape memory alloys. The substitution of Fe for Ni reduces the MT temperature of Ni-Fe-Mn-Al alloys effectively, and the magnetization of the austenite was significantly enhanced in these high-doped alloys. The Fe introduction converts antiferromagnetic austenite to ferrimagnetic state, and therefore, the unique MT occurs between ferrimagnetic and antiferromagnetic state in these alloys. The MT temperatures decreased by about 15 K under the magnetic field of 30 kOe for x = 8 alloy. The positive value of magnetic entropy change was determined to 3.35 J/kg K around the MT in the field change of 30 kOe for x = 6 alloy. These results suggest that Ni50- x Fe x Mn32Al18 alloys would be the promising candidates for magnetic multifunctional materials.

  12. Specific features of the electronic properties of Ti50Ni50- x Cu x alloys with the shape memory effect

    NASA Astrophysics Data System (ADS)

    Kourov, N. I.; Korolev, A. V.; Kuranova, N. N.; Pushin, V. G.

    2016-06-01

    The magnetic susceptibility, electrical resistivity, and thermoelectric power of Ti50Ni50‒ x Cu x alloys with copper concentrations x ⩽ 25 at % have been measured in the temperature range of 2-500 K. The change in the electronic band structure near the Fermi level upon thermoelastic martensitic transformations, such as B2 ↔ B19', B2 ↔ B19 ↔ B19', and B2 ↔ B19, has been considered.

  13. Hot Corrosion Behavior of Cold-Sprayed Ni-50Cr Coating in an Incinerator Environment at 900 °C

    NASA Astrophysics Data System (ADS)

    Singh, Harminder; Sidhu, T. S.; Kalsi, S. B. S.; Karthikeyan, J.

    2015-02-01

    In the present study, 50%Ni-50%Cr coating was developed on Superni 75 superalloy by a novel and facile cold-spray coating deposition technique. Dense, adhered, and oxide-free cold-sprayed coating was obtained in this study. This coating effectively provided corrosion protection to the substrate in real service incinerator conditions at 900 °C. The corrosion rate of the coated alloy was 0.47 mm/year, compared with 1.04 mm/year for bare alloy. This study indicates that the cold-spray process is an effective alternative for depositing high-temperature corrosion-resistant coatings.

  14. Suppression of the ferromagnetic order in the Heusler alloy Ni50Mn35In15 by hydrostatic pressure

    NASA Astrophysics Data System (ADS)

    Salazar Mejía, C.; Mydeen, K.; Naumov, P.; Medvedev, S. A.; Wang, C.; Hanfland, M.; Nayak, A. K.; Schwarz, U.; Felser, C.; Nicklas, M.

    2016-06-01

    We report on the effect of hydrostatic pressure on the magnetic and structural properties of the shape-memory Heusler alloy Ni50Mn35In15. Magnetization and x-ray diffraction experiments were performed at hydrostatic pressures up to 5 GPa using diamond anvil cells. Pressure stabilizes the martensitic phase, shifting the martensitic transition to higher temperatures, and suppresses the ferromagnetic austenitic phase. Above 3 GPa, where the martensitic-transition temperature approaches the Curie temperature in the austenite, the magnetization shows no longer indications of ferromagnetic ordering. We further find an extended temperature region with a mixture of martensite and austenite phases, which directly relates to the magnetic properties.

  15. First-principles description of phonons in Ni50 Pt50 disordered alloys: The role of relaxation

    NASA Astrophysics Data System (ADS)

    Ghosh, Subhradip; Neaton, J. B.; Antons, Armin H.; Cohen, Morrel H.; Leath, P. L.

    2004-07-01

    Using a combination of density-functional perturbation theory and the itinerant coherent potential approximation, we study the effects of atomic relaxation on the inelastic incoherent neutron scattering cross sections of disordered Ni50Pt50 alloys. We build on previous work, where empirical force constants were adjusted ad hoc to agree with experiment. After first relaxing all structural parameters within the local-density approximation for ordered NiPt compounds, density-functional perturbation theory is then used to compute phonon spectra, densities of states, and force constants. The resulting nearest-neighbor force constants are first compared to those of other ordered structures of different stoichiometry and then used to generate the inelastic scattering cross sections within the itinerant coherent potential approximation. We find that structural relaxation substantially affects the computed force constants and resulting inelastic cross sections, and that the effect is much more pronounced in random alloys than in ordered alloys.

  16. Premartensitic transition and relevant magnetic effects in Ni50Mn34In15.5Al0.5 alloy.

    PubMed

    Wu, Yuqin; Guo, Shaopu; Yu, Shuyun; Cheng, Hui; Wang, Ruilong; Xiao, Haibo; Xu, Lingfang; Xiong, Rui; Liu, Yong; Xia, Zhengcai; Yang, Changping

    2016-01-01

    Resistance measurement, in situ optical microscopic observation, thermal and magnetic measurements have been carried out on Ni50Mn34In15.5Al0.5 alloy. The existence of a pronounced premartensitic transition prior to martensitic transition can be characterized by microstructure evolution as well as exothermic peak and smooth decrease of resistance and magnetization with obvious hysteresis over a wide temperature range upon cooling. Consequently, the alloy undergoes two successive magneto-structural transitions consisting of premartensitic and martensitic transitions. Magnetoelastic coupling between magnetic and structural degrees of freedom would be responsible for the appearance of premartensitic transition, as evinced by the distinct shift of transitions temperatures to lower temperature with external applied field of 50 kOe. The inverse premartensitic transition induced by magnetic field results in large magnetoresistance, and contributes to the enhanced inverse magnetocaloric effect through enlarging the peak value and temperature interval of magnetic entropy change ΔSm. PMID:27183331

  17. Premartensitic transition and relevant magnetic effects in Ni50Mn34In15.5Al0.5 alloy

    NASA Astrophysics Data System (ADS)

    Wu, Yuqin; Guo, Shaopu; Yu, Shuyun; Cheng, Hui; Wang, Ruilong; Xiao, Haibo; Xu, Lingfang; Xiong, Rui; Liu, Yong; Xia, Zhengcai; Yang, Changping

    2016-05-01

    Resistance measurement, in situ optical microscopic observation, thermal and magnetic measurements have been carried out on Ni50Mn34In15.5Al0.5 alloy. The existence of a pronounced premartensitic transition prior to martensitic transition can be characterized by microstructure evolution as well as exothermic peak and smooth decrease of resistance and magnetization with obvious hysteresis over a wide temperature range upon cooling. Consequently, the alloy undergoes two successive magneto-structural transitions consisting of premartensitic and martensitic transitions. Magnetoelastic coupling between magnetic and structural degrees of freedom would be responsible for the appearance of premartensitic transition, as evinced by the distinct shift of transitions temperatures to lower temperature with external applied field of 50 kOe. The inverse premartensitic transition induced by magnetic field results in large magnetoresistance, and contributes to the enhanced inverse magnetocaloric effect through enlarging the peak value and temperature interval of magnetic entropy change ΔSm.

  18. Premartensitic transition and relevant magnetic effects in Ni50Mn34In15.5Al0.5 alloy

    PubMed Central

    Wu, Yuqin; Guo, Shaopu; Yu, Shuyun; Cheng, Hui; Wang, Ruilong; Xiao, Haibo; Xu, Lingfang; Xiong, Rui; Liu, Yong; Xia, Zhengcai; Yang, Changping

    2016-01-01

    Resistance measurement, in situ optical microscopic observation, thermal and magnetic measurements have been carried out on Ni50Mn34In15.5Al0.5 alloy. The existence of a pronounced premartensitic transition prior to martensitic transition can be characterized by microstructure evolution as well as exothermic peak and smooth decrease of resistance and magnetization with obvious hysteresis over a wide temperature range upon cooling. Consequently, the alloy undergoes two successive magneto-structural transitions consisting of premartensitic and martensitic transitions. Magnetoelastic coupling between magnetic and structural degrees of freedom would be responsible for the appearance of premartensitic transition, as evinced by the distinct shift of transitions temperatures to lower temperature with external applied field of 50 kOe. The inverse premartensitic transition induced by magnetic field results in large magnetoresistance, and contributes to the enhanced inverse magnetocaloric effect through enlarging the peak value and temperature interval of magnetic entropy change ΔSm. PMID:27183331

  19. Face-related segregation reversal at Pt 50Ni 50 surfaces studied with the embedded atom method

    NASA Astrophysics Data System (ADS)

    Deurinck, P.; Creemers, C.

    1999-11-01

    The segregation to the three low-index surfaces of a Pt50Ni50 single crystal is modelled by Monte Carlo simulations combined with the embedded atom method (EAM). Using the best fit EAM parameters from the literature for the six transition metals of the Ni and Cu groups does not yield satisfactory results. In this work the EAM parameters are recalculated and optimised exclusively for the Pt-Ni alloy system under study. Only then does EAM reliably reproduce the driving forces for segregation. The experimental results [Y. Gauthier et al., Phys. Rev. B 31 (1985) 6216; Y. Gauthier et al., Phys. Rev. B 35 (1987) 7867; S.M. Foiles, in: P.A. Dobson, A. Miller (Eds.), Surface Segregation Phenomena, CRC Press, Boca Raton, FL, 1990, p. 79] reveal a face-related segregation reversal for the Pt50Ni50 single crystal. It appears from the simulations that this is caused by a relatively small difference in surface energy in close competition with the elastic strain release. At the open (110) surface the difference in surface energy dominates causing Ni segregation. At the (100) and (111) surfaces the difference in surface energy is overpowered by the elastic strain leading to Pt segregation. The simulations are in good agreement with the experimental results and reproduce quantitatively the Ni segregation to the (110) surface and the Pt segregation to the (100) and (111) surfaces. Only at the (110) surface significant relaxations are predicted in good agreement with experimental evidence. Atomic vibrations can be included by allowing a large number of very small displacements or with a more classical treatment of vibrational entropy. Both approaches yield the same results and show that the inclusion of atomic vibrations is important only for the (110) surface and tend to attenuate the Ni segregation profile.

  20. Magneto-structural transformations in Ni50Mn37.5Sn12.5-xInx Heusler powders

    NASA Astrophysics Data System (ADS)

    Maziarz, Wojciech; Wójcik, Anna; Czaja, Paweł; Żywczak, Antoni; Dutkiewicz, Jan; Hawełek, Łukasz; Cesari, Eduard

    2016-08-01

    The effect of ball milling and subsequently annealing of melt spun ribbons on magneto-structural transformations in Ni50Mn37.5Sn12.5-xInx (x=0, 2, 4, 6) ribbons is presented. Short time vibration milling allows to obtain chemically homogenous powders of angular particle shapes and size within 10-50 μm. Milling does not change the characteristic temperatures of martensitic transformation in comparison to the melt spun ribbons. The effect of In substitution for Sn on martensitic transformation has a complex mechanism, associated with electron density change. Substitution of Sn by In in both milled and annealed powders leads to decrease of Curie temperature of austenite and increase of martensitic transformation temperature, stabilizing martensitic phase. The coexistence of magnetic transformation of austenite and martensitic transformation at low magnetic field was observed. The intermartensitic transformation of 4O martensite to L10 martensite was observed during cooling at low magnetic field and this was confirmed by TEM microstructure observations. The annealing process of as-milled powders leads to the change of their martensitic structure due to relaxation of internal stresses associated with anisotropic columnar grain microstructure formed during melt spinning process. The level of stresses introduced during milling of ribbons has no significant influence on martensitic transformation. The annealing process of as milled powders leads to enhancement of their magnetic properties, decrease of Curie temperature of austenite, and marginal change of temperature of martenisitic transformation.

  1. Coexistance of magnetoelectric effect and exchange bias in Ni50.3Mn36.9Sb12.8/BiFeO3 heterostructure thin film

    NASA Astrophysics Data System (ADS)

    Barman, Rahul; Kaur, Davinder

    2016-05-01

    In the present study structural, magnetic and ferroelectric properties of Ni50.3Mn36.9Sb12.8/BiFeO3 heterostructure thin film, grown on LaNiO3 coated Si (100) substrate has been systematically investigated. Ni50.3Mn36.9Sb12.8 film exhibits L21 structure with preferred (220) orientation. The bottom LaNiO3 layer was implemented to favor the growth of pervoskite BiFeO3 film with (l00) orientation. The shift in hysteresis loop up to 34 Oe from the origin was observed at 300 K which is mainly due to the coupling of FM-AFM spins at the interface. Besides the exchange bias effect, large coupling between ferromagnetic and ferroelectric order parameters was also found with maximum coupling sensitivity of 7.58 V/cm-Oe at 300K in Ni50.3Mn36.9Sb12.8/BiFeO3 heterostructure thin film. The observed magneto-electric effect in this heterostructure is due to the transfer of strain from ferromagnetic shape memory alloy Ni50.3Mn36.9Sb12.8 layer to multiferroic BiFeO3 layer in the presence of magnetic field. Hence, coexistence of magneto-electric coupling and exchange bias in Ni50.3Mn36.9Sb12.8/BiFeO3 heterostructure make them a promising candidate for various multifunctional MEMS devices.

  2. Amorphic complexity

    NASA Astrophysics Data System (ADS)

    Fuhrmann, G.; Gröger, M.; Jäger, T.

    2016-02-01

    We introduce amorphic complexity as a new topological invariant that measures the complexity of dynamical systems in the regime of zero entropy. Its main purpose is to detect the very onset of disorder in the asymptotic behaviour. For instance, it gives positive value to Denjoy examples on the circle and Sturmian subshifts, while being zero for all isometries and Morse-Smale systems. After discussing basic properties and examples, we show that amorphic complexity and the underlying asymptotic separation numbers can be used to distinguish almost automorphic minimal systems from equicontinuous ones. For symbolic systems, amorphic complexity equals the box dimension of the associated Besicovitch space. In this context, we concentrate on regular Toeplitz flows and give a detailed description of the relation to the scaling behaviour of the densities of the p-skeletons. Finally, we take a look at strange non-chaotic attractors appearing in so-called pinched skew product systems. Continuous-time systems, more general group actions and the application to cut and project quasicrystals will be treated in subsequent work.

  3. Giant spontaneous exchange bias triggered by crossover of superspin glass in Sb-doped Ni50Mn38Ga12 Heusler alloys.

    PubMed

    Tian, Fanghua; Cao, Kaiyan; Zhang, Yin; Zeng, Yuyang; Zhang, Rui; Chang, Tieyan; Zhou, Chao; Xu, Minwei; Song, Xiaoping; Yang, Sen

    2016-01-01

    A spontaneous exchange bias (SEB) discovered by Wang et al. [Phys. Rev. Lett. 106 (2011) 077203.] after zero-field cooling (ZFC) has attracted recent attention due to its interesting physics. In this letter, we report a giant SEB tuned by Sb-doping in Ni50Mn38Ga12-xSbx Heusler alloys. Such an SEB was switched on below the blocking temperature of approximately 50 K. The maximum exchange bias HE can arrive at 2930 Oe in a Ni50Mn38Ga10Sb2 sample after ZFC to 2 K. Further studies showed that this SEB was attributable to interaction of superspin glass (SSG) and antiferromagnetic matix, which was triggered by the crossover of SSG from canonical spin glass to a cluster spin glass. Our results not only explain the underlying physics of SEB, but also provide a way to tune and control the SEB performance.

  4. Giant spontaneous exchange bias triggered by crossover of superspin glass in Sb-doped Ni50Mn38Ga12 Heusler alloys.

    PubMed

    Tian, Fanghua; Cao, Kaiyan; Zhang, Yin; Zeng, Yuyang; Zhang, Rui; Chang, Tieyan; Zhou, Chao; Xu, Minwei; Song, Xiaoping; Yang, Sen

    2016-01-01

    A spontaneous exchange bias (SEB) discovered by Wang et al. [Phys. Rev. Lett. 106 (2011) 077203.] after zero-field cooling (ZFC) has attracted recent attention due to its interesting physics. In this letter, we report a giant SEB tuned by Sb-doping in Ni50Mn38Ga12-xSbx Heusler alloys. Such an SEB was switched on below the blocking temperature of approximately 50 K. The maximum exchange bias HE can arrive at 2930 Oe in a Ni50Mn38Ga10Sb2 sample after ZFC to 2 K. Further studies showed that this SEB was attributable to interaction of superspin glass (SSG) and antiferromagnetic matix, which was triggered by the crossover of SSG from canonical spin glass to a cluster spin glass. Our results not only explain the underlying physics of SEB, but also provide a way to tune and control the SEB performance. PMID:27478090

  5. Giant spontaneous exchange bias triggered by crossover of superspin glass in Sb-doped Ni50Mn38Ga12 Heusler alloys

    PubMed Central

    Tian, Fanghua; Cao, Kaiyan; Zhang, Yin; Zeng, Yuyang; Zhang, Rui; Chang, Tieyan; Zhou, Chao; Xu, Minwei; Song, Xiaoping; Yang, Sen

    2016-01-01

    A spontaneous exchange bias (SEB) discovered by Wang et al. [Phys. Rev. Lett. 106 (2011) 077203.] after zero-field cooling (ZFC) has attracted recent attention due to its interesting physics. In this letter, we report a giant SEB tuned by Sb-doping in Ni50Mn38Ga12-xSbx Heusler alloys. Such an SEB was switched on below the blocking temperature of approximately 50 K. The maximum exchange bias HE can arrive at 2930 Oe in a Ni50Mn38Ga10Sb2 sample after ZFC to 2 K. Further studies showed that this SEB was attributable to interaction of superspin glass (SSG) and antiferromagnetic matix, which was triggered by the crossover of SSG from canonical spin glass to a cluster spin glass. Our results not only explain the underlying physics of SEB, but also provide a way to tune and control the SEB performance. PMID:27478090

  6. Giant spontaneous exchange bias triggered by crossover of superspin glass in Sb-doped Ni50Mn38Ga12 Heusler alloys

    NASA Astrophysics Data System (ADS)

    Tian, Fanghua; Cao, Kaiyan; Zhang, Yin; Zeng, Yuyang; Zhang, Rui; Chang, Tieyan; Zhou, Chao; Xu, Minwei; Song, Xiaoping; Yang, Sen

    2016-08-01

    A spontaneous exchange bias (SEB) discovered by Wang et al. [Phys. Rev. Lett. 106 (2011) 077203.] after zero-field cooling (ZFC) has attracted recent attention due to its interesting physics. In this letter, we report a giant SEB tuned by Sb-doping in Ni50Mn38Ga12-xSbx Heusler alloys. Such an SEB was switched on below the blocking temperature of approximately 50 K. The maximum exchange bias HE can arrive at 2930 Oe in a Ni50Mn38Ga10Sb2 sample after ZFC to 2 K. Further studies showed that this SEB was attributable to interaction of superspin glass (SSG) and antiferromagnetic matix, which was triggered by the crossover of SSG from canonical spin glass to a cluster spin glass. Our results not only explain the underlying physics of SEB, but also provide a way to tune and control the SEB performance.

  7. Synthesis and Characterization of Bimetallic Ni50Pt50 Catalyst Supported on SiO2 for N2O Decomposition.

    PubMed

    Angeles-Pascual, A; Esparza, R; Tellez-Vazquez, O; Velumani, S; Pérez, R

    2015-12-01

    Nanometallic and bimetallic catalyst of Ni, Pt and Ni50Pt50 were studied by the decompositions of N2O. The catalyst were prepared by incipient wetness impregnation of the silica with low superficial area of 50 m2/g supported with aqueous solution of the metal precursors, for Pt H2Pt Cl6 x 6H2O was used and for Ni, Ni(NO3)2 was used to a total metal loading of 1% wt. Catalyst were oxidized for 2 hours at 400 degrees C with O2, then the samples were reduced for 30 minutes with N2 and 2 hours with H2, all at the same temperature. The catalyst was characterized by Transmission Electron Microscopy (TEM), High Angular Annular Dark Field (HAADF), High Resolution Transmission Electron Microscopy (HR-TEM) and Termoprogramed Reduction (TPR). The mean particle sizes obtained by TEM and HAADF were about 12.5 nm for Ni/SiO2, 2.8 nm for Pt/SiO2 and 3.5 nm Ni50Pt50/SiO2 catalysts respectability. HR-TEM and HAADF analysis showed differences between Ni and Pt catalysts displaying mainly cuboctahedral shapes. Stepped surface defects were found in the Ni50Pt50/SiO2 catalyst. Finally Ni50Pt50/SiO2 was more active than Pt/SiO2 and Ni/SiO2 catalysts for the decomposition of N2O. PMID:26682368

  8. A Comparative Study of Ni49.9Ti50.1 and Ni50.3Ti29.7Hf20 Tube Actuators

    NASA Astrophysics Data System (ADS)

    Owusu-Danquah, J. S.; Saleeb, A. F.; Dhakal, B.; Padula, S. A.

    2015-04-01

    A shape memory alloy (SMA) actuator typically has to operate for a large number of thermomechanical cycles due to its application requirements. Therefore, it is necessary to understand the cyclic behavioral response of the SMA actuation material and the devices into which they are incorporated under extended cycling conditions. The present work is focused on the nature of the cyclic, evolutionary behavior of two widely used SMA actuator material systems: (1) a commercially available Ni49.9Ti50.1, and (2) a developmental high-temperature Ni50.3Ti29.7Hf20 alloy. Using a recently developed general SMA modeling framework that utilizes multiple inelastic mechanisms, differences and similarities between the two classes of materials are studied, accounting for extended number of thermal cycles under a constant applied tensile/compressive force and under constant applied torque loading. From the detailed results of the simulations, there were significant qualitative differences in the evolution of deformation responses for the two different materials. In particular, the Ni49.9Ti50.1 tube showed significant evolution of the deformation response, whereas the Ni50.3Ti29.7Hf20 tube stabilized quickly. Moreover, there were significant differences in the tension-compression-shear asymmetry properties in the two materials. More specifically, the Ni50.3Ti29.7Hf20 tube exhibited much higher asymmetry effects, especially at low stress levels, compared to the Ni49.9Ti50.1. For both SMA tubes, the evolution of the deformation response under thermal cycling typically exhibited regions of initial transients, and subsequent evolution.

  9. Appearance of metastable B2 phase during solidification of Ni50Zr50 alloy: electrostatic levitation and molecular dynamics simulation studies.

    PubMed

    Quirinale, D G; Rustan, G E; Wilson, S R; Kramer, M J; Goldman, A I; Mendelev, M I

    2015-03-01

    High-energy x-ray diffraction measurements of undercooled, electrostatically levitated Ni50Zr50 liquid droplets were performed. The observed solidification pathway proceeded through the nucleation and growth of the metastable B2 phase, which persisted for several seconds before the rapid appearance of the stable B33 phase. This sequence is shown to be consistent with predictions from classical nucleation theory using data obtained from molecular dynamics (MD) simulations. A plausible mechanism for the B2-B33 transformation is proposed and investigated through further MD simulations. PMID:25650946

  10. Infrared Brazing of Ti50Ni50 Shape Memory Alloy and 316L Stainless Steel with Two Sliver-Based Fillers

    NASA Astrophysics Data System (ADS)

    Shiue, Ren-Kae; Chen, Chia-Pin; Wu, Shyi-Kaan

    2015-06-01

    Dissimilar infrared brazing Ti50Ni50 and AISI 316L stainless steel using two silver-based fillers, Cusil-ABA and Ticusil, was evaluated. The shear strength of the Ticusil brazed joint is higher than that of the Cusil-ABA brazed one due to the formation of better fillet. The maximum shear strength of 237 MPa is obtained for the Ticusil joint brazed at 1223 K (950 °C) for 60 seconds. The presence of interfacial Ti-Fe-(Cu) layer is detrimental to the shear strength of all joints.

  11. Amorphous metal composites

    DOEpatents

    Byrne, Martin A.; Lupinski, John H.

    1984-01-01

    An improved amorphous metal composite and process of making the composite. The amorphous metal composite comprises amorphous metal (e.g. iron) and a low molecular weight thermosetting polymer binder. The process comprises placing an amorphous metal in particulate form and a thermosetting polymer binder powder into a container, mixing these materials, and applying heat and pressure to convert the mixture into an amorphous metal composite.

  12. Characterization and High-Temperature Oxidation Behavior of Cold-Sprayed Ni-20Cr and Ni-50Cr Coatings on Boiler Steels

    NASA Astrophysics Data System (ADS)

    Bala, Niraj; Singh, Harpreet; Prakash, Satya

    2011-11-01

    Microstructure and mechanical properties of cold-spray coatings are usually required in order to explore the potential industrial application of the latter. This article demonstrates the successful formulation of Ni-20Cr and Ni-50Cr coatings on two boiler steels, namely, SAE 213-T22 and SA 516 steel by cold-spray process. The microstructure, coating thickness, phase formation, and microhardness properties of the coatings were evaluated. The coatings were subjected to cyclic heating and cooling cycles at an elevated temperature of 1173.15 K (900 °C) to ascertain their high-temperature oxidation behavior. Moreover, these cyclic exposures can give useful information regarding the adhesion of the coatings with the substrate steels. Of all the coatings, the Ni-50Cr coating on SA 516 steel had a maximum average hardness value of 469 Hv. As observed from the surface field emission-scanning electron microscopy (FE-SEM) analysis, the coatings were found to have nearly dense microstructure with the sprayed particles in interlocked positions. It was concluded that the cold-spray process is suitable for spraying the preceding powders onto the given boiler steels to produce nearly dense and low oxide coatings. The coatings, in general, were found to follow the parabolic rate of oxidation and were successful in maintaining their surface contact with their respective substrate steels.

  13. High-temperature oxidation studies of cold-sprayed Ni-20Cr and Ni-50Cr coatings on SAE 213-T22 boiler steel

    NASA Astrophysics Data System (ADS)

    Bala, Niraj; Singh, Harpreet; Prakash, Satya

    2009-05-01

    The high-temperature oxidation behavior of cold-sprayed Ni-20Cr and Ni-50Cr coatings on SAE 213-T22 boiler steel has been investigated at 900 °C in air under cyclic heating and cooling conditions for 50 cycles. The kinetics of oxidation of coated and bare boiler steel has been established with the help of weight change measurements. It was observed that all the coated and bare steels obeyed parabolic rate law of oxidation. X-ray diffraction, FE-SEM/EDAX and X-ray mapping techniques were used to analyse the oxidation products of the coated and uncoated boiler steel. The uncoated steel suffered corrosion in the form of intense spalling and peeling of its oxide scale, which was perhaps due to the formation of unprotective Fe 2O 3 oxide scale. Both the coatings showed better resistance to the air oxidation as compared to the uncoated steel. The Ni-50Cr coating was found to be more protective than the Ni-20Cr-coated steel. The formation of oxides and spinels of nickel and chromium may be contributing to the development of air oxidation resistance in the coatings.

  14. Study of the dynamical features of the austenite-martensite phase transition in the Ni50(Mn, 1%Fe)34In16 alloy using scanning Hall probe imaging

    NASA Astrophysics Data System (ADS)

    Chattopadhyay, M. K.; Morrison, K.; Dupas, A.; Sharma, V. K.; Sharath Chandra, L. S.; Cohen, L. F.; Roy, S. B.

    2012-03-01

    We have performed scanning Hall probe imaging experiments to study the martensite to austenite phase transition in the Ni50(Mn, 1%Fe)34In16 alloy as a function of temperature and magnetic field. We observe that the martensite and austenite phase regions are separated by a distinct interface. The relative growth of phase across the phase transition is associated with the movement of this interface. The movement of the interface becomes arrested at low temperature, which leads to the formation of a "magnetic glass" state in the alloy. The dynamics of the martensite to austenite phase transition in the Ni50(Mn, 1%Fe)34In16 alloy is found to be qualitatively different when the transition is field induced than what it is when the same transition is induced by temperature. While both nucleation and growth of the martensite phase is observed during the austenite to martensite phase transition in the alloy during cooling down, the martensite to austenite phase transition during warming up appears to be growth oriented. In contrast, both nucleation and growth of the product phases are observed during the field induced martensite to austenite phase transition both during increasing and decreasing field experiments. The physical reasons behind these different observations are explored.

  15. Large spontaneous exchange bias and giant magnetoresistance in Ni50Mn37-xFexIn13(x=2-4) Heusler alloys

    NASA Astrophysics Data System (ADS)

    Jing, Chao; Liu, Yang; Zheng, Dong; Wang, Xiaolong; Sun, Junkun; Zhang, Yuanlei; Liu, Changqin; Deng, Dongmei; Feng, Zhenjie; Xu, Kun; Li, Zhe

    2016-09-01

    In the present work, we have obtained a large zero-field cooled exchange-bias (spontaneous exchange bias, SEB) in Ni50Mn35Fe2In13 Heusler alloy. The experimental results indicate that the sample with x=2 exhibits super-spin glass (SSG), super-paramagnetic (SPM), super-ferromagnetic (SFM) and antiferromagnetic (AFM) behaviors in the martensite state at low temperature. Contributing to the complex magnetic interactions, a large SEB effect with the value of 1567 Oe was obtained at 5 K. At the same time, a non-monotonic behavior of spontaneous exchange bias field (spontaneous HEB) was observed with the variation of temperature, which is resulted from the competition between the volume fraction of SFM clusters and the exchange coupling of the SFM-AFM interface. In addition, during martensitic transformation (MT), extraordinary electrical transport properties of Ni50Mn37-xFexIn13 (x=2-4) alloys have been observed under various external magnetic field. The maximal value of the giant magnetoresistance (GMR) reaches about 57% at 135 K under the external magnetic field change of 50 kOe. The effect of field induced reverse martensitic transformation (FIRMT) on the GMR has been also discussed.

  16. The effect of substitution of Mn by Fe and Cr on the martensitic transition in the Ni50Mn34In16 alloy.

    PubMed

    Sharma, V K; Chattopadhyay, M K; Nath, S K; Sokhey, K J S; Kumar, R; Tiwari, P; Roy, S B

    2010-12-01

    The potential shape memory alloy Ni(50)Mn(34)In(16) is studied with partial substitution of Mn with Fe and Cr to investigate the effect of such substitution on the martensitic transition in the Ni-Mn-In alloy system. The results of ac susceptibility, magnetization and electrical resistivity measurements show that while the substitution with Cr increases the martensitic transition temperature, the substitution with Fe decreases it. Possible reasons for this shift in martensitic transition are discussed. Evidence of kinetic arrest of the austenite to martensite phase transition in the Fe substituted alloys is also presented. Unlike the kinetic arrest of the austenite to martensite phase transition in the parent Ni(50)Mn(34)In(16) alloy which takes place in the presence of high external magnetic field, the kinetic arrest of the austenite to martensite phase transition in the Fe doped alloy occurs even in zero magnetic field. The Cr substituted alloys, on the other hand, show no signature of kinetic arrest of this phase transition.

  17. The effect of Pd on martensitic transformation and magnetic properties for Ni50Mn38-xPdxSn12Heusler alloys

    NASA Astrophysics Data System (ADS)

    Jing, C.; Zheng, D.; Li, Z.; Yu, L. J.; Zhang, Y. L.; Liu, Y.; Sun, J. K.; Liu, C. Q.; Deng, D. M.; Yang, W. T.

    2016-05-01

    In the past decade, Mn rich Ni-Mn based alloys have attained considerable attention due to their abundant physics and potential application as multifunctional materials. In this paper, polycrystalline Ni50Mn38-xPdxSn12 (x = 0, 2, 4, 6) Heusler alloys have been prepared, and the martensitic phase transformation (MPT) together with the shape memory effect and the magnetocaloric effect has been investigated. The experimental result indicates that the MPT evidently shifts to a lower temperature with increase of Pd substitution for Mn atoms, which can be attributed to the weakness of the hybridization between the Ni atom and excess Mn on the Sn site rather than the electron concentration. The physics properties study focused on the sample of Ni50Mn34Pd4Sn12 shows a good two-way shape memory behavior, and the maximum value of strain Δ L/L reaches about 0.13% during the MPT. The small of both entropy change Δ ST and magnetostrain can be ascribed to the inconspicuous influence of magnetic field induced MPT.

  18. Amorphous Computing

    NASA Astrophysics Data System (ADS)

    Sussman, Gerald

    2002-03-01

    agents constructed by engineered cells, but we have few ideas for programming them effectively: How can one engineer prespecified, coherent behavior from the cooperation of immense numbers of unreliable parts that are interconnected in unknown, irregular, and time-varying ways? This is the challenge of Amorphous Computing.

  19. Skeletal Ni Catalysts Prepared from Amorphous Ni-Zr Alloys: Enhanced Catalytic Performance for Hydrogen Generation from Ammonia Borane.

    PubMed

    Nozaki, Ai; Tanihara, Yasutomo; Kuwahara, Yasutaka; Ohmichi, Tetsutaro; Mori, Kohsuke; Nagase, Takeshi; Yasuda, Hiroyuki Y; Yamashita, Hiromi

    2016-02-01

    Skeletal Ni catalysts were prepared from Ni-Zr alloys, which possess different chemical composition and atomic arrangements, by a combination of thermal treatment and treatment with aqueous HF. Hydrogen generation from ammonia borane over the skeletal Ni catalysts proceeded efficiently, whereas the amorphous Ni-Zr alloy was inactive. Skeletal Ni prepared from amorphous Ni30 Zr70 alloy had a higher catalytic activity than that prepared from amorphous Ni40 Zr60 and Ni50 Zr50 alloys. The atomic arrangement of the Ni-Zr alloy also strongly affected the surface structure and catalytic activities. Thermal treatment of the amorphous Ni-Zr alloys at a temperature slightly lower than the crystallization temperature led to an increase of the number of surface-exposed Ni atoms and an enhancement of the catalytic activities for hydrogen generation from ammonia borane. The skeletal Ni catalysts also showed excellent durability and recyclability.

  20. Constant-Strain Thermal Cycling of a Ni50.3Ti29.7Hf20 High-Temperature Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Benafan, O.; Noebe, R. D.; Halsmer, T. J.; Padula, S. A.; Bigelow, G. S.; Gaydosh, D. J.; Garg, A.

    2016-06-01

    The effect of various pre-straining routines on the recovery stresses of a Ni-rich Ni50.3Ti29.7Hf20 high-temperature shape memory alloy was investigated in tension and compression. The recovery stresses, obtained by means of constant-strain thermal cycling, were evaluated after isothermal (up to ±2 % applied strain at room temperature) or after isobaric thermal cycling at stress levels between ±100 and 400 MPa. The material exhibited high force generation capability with recovery stresses of nearly 1.5 GPa on the first cycle under particular pre-strain conditions. The recovery stresses are shown to decay during subsequent cycles using an upper cycle temperature of 300 °C with a saturated stress level nearing 1.1 GPa in compression.

  1. Internal friction associated with the premartensitic transformation and twin boundary motion of Ni50+xMn25-xGa25 (x = 0-2) alloys

    NASA Astrophysics Data System (ADS)

    Liu, Junyi; Wang, Jingmin; Jiang, Chengbao; Xu, Huibin

    2013-03-01

    The internal friction (IF) during the martensitic transformation (MT) has been extensively studied in NiMnGa alloys. In this paper, temperature dependence of the IF associated with the premartensitic transformation (PMT) and twin boundary motion (TBM) was investigated in Ni50+xMn25-xGa25 (x = 0-2) alloys. Both the composition and frequency had no obvious effect on the IF peak position of the PMT and TBM. With increasing frequency from 0.1 Hz to 5 Hz, the IF peak height corresponding to the TBM was significantly decreased, but was kept constant during the PMT. The observed phenomena were discussed in terms of the different microscopic mechanisms of the TBM and PMT.

  2. Effect of Aging Treatment on Superelasticity of a Ti48.8Ni50.8V0.4 Alloy

    NASA Astrophysics Data System (ADS)

    Zhao, H.; Liang, C. Q.; Liu, J. T.; Tong, Y. X.; Chen, F.; Tian, B.; Li, L.; Zheng, Y. F.

    2012-12-01

    In this study, effect of aging treatment on microstructure, deformation behavior, and superelasticity of Ti48.8Ni50.8V0.4 alloy was investigated. After aging at 400 °C for 30 min, Ti3Ni4 precipitates formed. With increasing aging temperature from 300 to 450 °C, the yield strength of reoriented martensite increased due to the strengthening effect of Ti3Ni4 phase, thus improved the shape recovery ratio and reduced the stress hysteresis. Further increasing the aging temperature, the size of Ti3Ni4 precipitates increased and the coherency between precipitate and matrix gradually lost, leading to the decreasing yield strength of reoriented martensite and shape recovery ratio. Simultaneously, the stress hysteresis increased resulting from the hinder of plastic deformation to the interfacial movement during phase transformation. The critical stress to induce martensitic transformation continuously decreased with increasing aging temperature.

  3. Multiferroic tunnel junction of Ni50.3Mn36.9Sb12.8/BiFeO3/Ni50.3Mn36.9Sb12.8 for magneto-electric random access memory devices

    NASA Astrophysics Data System (ADS)

    Barman, Rahul; Kaur, Davinder

    2016-02-01

    A multiferroic tunnel junction composed of two ferromagnetic shape memory alloy electrodes separated by a multiferroic barrier was fabricated from a Ni50.3Mn36.9Sb12.8/BiFeO3/Ni50.3Mn36.9Sb12.8 trilayer. A large exchange bias field (HEB) of ˜59 Oe at room temperature was found for this trilayer. Besides the exchange bias effect in this multiferroic tunnel junction, one of the most interesting results was the magnetoelectric effect, which is manifested by the transfer of strain from the Ni50.3Mn36.9Sb12.8 electrodes to the BiFeO3 tunnel barrier. The magnetic field dependence of the junction resistance was observed at room temperature after aligning the ferroelectric polarization of the BiFeO3 barrier with the poling voltage of ±3 V. A change in junction resistance was also observed between the magnetic parallel and antiparallel states of the electrodes, suggesting an entire flip of the magnetic domains against the magnetic field. After reversing the polarization of the BiFeO3 barrier between the two directions, the entire R-H curve was shifted so that both parallel and antiparallel resistances switched to different values. Hence, after applying positive and negative voltages, two parallel and two antiparallel states, i.e., four distinct states were observed. These four states will encode quaternary information by both ferromagnetic and ferroelectric order-parameters, to read non-destructively by resistance measurement. These findings may be helpful towards reconfigurable logic spintronics architectures in next generation magneto-electric random access memory devices.

  4. Nanocrystal dispersed amorphous alloys

    NASA Technical Reports Server (NTRS)

    Perepezko, John H. (Inventor); Allen, Donald R. (Inventor); Foley, James C. (Inventor)

    2001-01-01

    Compositions and methods for obtaining nanocrystal dispersed amorphous alloys are described. A composition includes an amorphous matrix forming element (e.g., Al or Fe); at least one transition metal element; and at least one crystallizing agent that is insoluble in the resulting amorphous matrix. During devitrification, the crystallizing agent causes the formation of a high density nanocrystal dispersion. The compositions and methods provide advantages in that materials with superior properties are provided.

  5. Microwave absorption properties of lightweight absorber based on Fe50Ni50-coated poly(acrylonitrile) microspheres and reduced graphene oxide composites

    NASA Astrophysics Data System (ADS)

    Zhang, Bin; Wang, Jun; Wang, Junpeng; Huo, Siqi; Zhang, Bin; Tang, Yushan

    2016-09-01

    In this paper, we proposed a facile method to obtain the lightweight composites consisting of surface modified Fe50Ni50-coated poly(acrylonitrile) microspheres (PANS@SMF), reduced graphene oxide (RGO) and epoxy resin. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM) and vector network analyzer (VNA). Impedance matching condition and electromagnetic wave attenuation characteristic were used for the reflection loss (RL) performance of the composites. Compared with pure PANS@SMF and RGO composites, the -10 dB absorption bandwidth and the minimum RL of the hybrid composites were enhanced. The bandwidth less than -10 dB was almost 4.5 GHz in the range of 10 GHz to 14.5 GHz, with a matching thickness of 2.5 mm. The density of the hybrid composites was in the range of 0.25-0.34 g/cm3. Therefore, the hybrid composite can be considered as a potential lightweight microwave absorber.

  6. On the Recovery Stress of a Ni50.3Ti29.7Hf20 High Temperature Shape Memory Alloy

    NASA Technical Reports Server (NTRS)

    Benafan, O.; Noebe, R. D.; Padula, S. A., II; Bigelow, G. S.; Gaydosh, D. J.; Garg, A.; Halsmer, T. J.

    2015-01-01

    Recovery stress in shape memory alloys (SMAs), also known as blocking stress, is an important property generally obtained during heating under a dimensional constraint as the material undergoes the martensitic phase transformation. This property has been instinctively utilized in most SMA shape-setting procedures, and has been used in numerous applications such as fastening and joining, rock splitting, safety release mechanisms, reinforced composites, medical devices, and many other applications. The stress generation is also relevant to actuator applications where jamming loads (e.g., in case the actuator gets stuck and is impeded from moving) need to be determined for proper hardware sizing. Recovery stresses in many SMA systems have been shown to reach stresses in the order of 800 MPa, achieved via thermo-mechanical training such as pre-straining, heat treatments or other factors. With the advent of high strength, high temperature SMAs, recovery stress data has been rarely probed, and there is no information pertinent to the magnitudes of these stresses. Thus, the purpose of this work is to investigate the recovery stress capability of a precipitation strengthened, Ni50.3Ti29.7Hf20 (at.) high temperature SMA in uniaxial tension and compression. This material has been shown to exhibit outstanding strength and stability during constant-stress, thermal cycling, but no data exists on constant-strain thermal cycling. Several training routines were implemented as part of this work including isothermal pre-straining, isobaric thermal cycling, and isothermal cyclic training routines. Regardless of the training method used, the recovery stress was characterized using constant-strain (strain-controlled condition) thermal cycling between the upper and lower cycle temperatures. Preliminary results indicate recovery stresses in excess of 1.5 GPa were obtained after a specific training routine. This stress magnitude is significantly higher than conventional NiTi stress

  7. Small-angle neutron scattering study of magnetic ordering and inhomogeneity across the martensitic phase transformation in Ni50–xCoxMn₄₀Sn₁₀ alloys

    DOE PAGES

    Bhatti, Kanwal Preet; El-Khatib, S.; Srivastava, Vijay; James, R. D.; Leighton, C.

    2012-04-27

    The Heusler-derived multiferroic alloy Ni50–xCoxMn₄₀Sn₁₀ has recently been shown to exhibit, at just above room temperature, a highly reversible martensitic phase transformation with an unusually large magnetization change. In this work the nature of the magnetic ordering above and below this transformation has been studied in detail in the critical composition range x = 6–8 via temperature-dependent (5–600 K) magnetometry and small-angle neutron scattering (SANS). We observe fairly typical paramagnetic to long-range-ordered ferromagnetic phase transitions on cooling to 420–430 K, with the expected critical spin fluctuations, followed by first-order martensitic phase transformations to a nonferromagnetic state below 360–390 K. Themore » static magnetization reveals complex magnetism in this low-temperature nonferromagnetic phase, including a Langevin-like field dependence, distinct spin freezing near 60 K, and significant exchange bias effects, consistent with superparamagnetic blocking of ferromagnetic clusters of nanoscopic dimensions. We demonstrate that these spin clusters, whose existence has been hypothesized in a variety of martensitic alloys exhibiting competition between ferromagnetic and antiferromagnetic exchange interactions, can be directly observed by SANS. The scattering data are consistent with a liquidlike spatial distribution of interacting magnetic clusters with a mean center-to-center spacing of 12 nm. Considering the behavior of the superparmagnetism, cooling-field and temperature-dependent exchange bias, and magnetic SANS, we discuss in detail the physical form and origin of these spin clusters, their intercluster interactions, the nature of the ground-state magnetic ordering in the martensitic phase, and the implications for our understanding of such alloy systems.« less

  8. Hydrogen in amorphous silicon

    SciTech Connect

    Peercy, P. S.

    1980-01-01

    The structural aspects of amorphous silicon and the role of hydrogen in this structure are reviewed with emphasis on ion implantation studies. In amorphous silicon produced by Si ion implantation of crystalline silicon, the material reconstructs into a metastable amorphous structure which has optical and electrical properties qualitatively similar to the corresponding properties in high-purity evaporated amorphous silicon. Hydrogen studies further indicate that these structures will accomodate less than or equal to 5 at.% hydrogen and this hydrogen is bonded predominantly in a monohydride (SiH/sub 1/) site. Larger hydrogen concentrations than this can be achieved under certain conditions, but the excess hydrogen may be attributed to defects and voids in the material. Similarly, glow discharge or sputter deposited amorphous silicon has more desirable electrical and optical properties when the material is prepared with low hydrogen concentration and monohydride bonding. Results of structural studies and hydrogen incorporation in amorphous silicon were discussed relative to the different models proposed for amorphous silicon.

  9. Trehalose amorphization and recrystallization.

    PubMed

    Sussich, Fabiana; Cesàro, Attilio

    2008-10-13

    The stability of the amorphous trehalose prepared by using several procedures is presented and discussed. Amorphization is shown to occur by melting (T(m)=215 degrees C) or milling (room temperature) the crystalline anhydrous form TRE-beta. Fast dehydration of the di-hydrate crystalline polymorph, TRE-h, also produces an amorphous phase. Other dehydration procedures of TRE-h, such as microwave treatment, supercritical extraction or gentle heating at low scan rates, give variable fractions of the polymorph TRE-alpha, that undergo amorphization upon melting (at lower temperature, T(m)=130 degrees C). Additional procedures for amorphization, such as freeze-drying, spray-drying or evaporation of trehalose solutions, are discussed. All these procedures are classified depending on the capability of the undercooled liquid phase to undergo cold crystallization upon heating the glassy state at temperatures above the glass transition temperature (T(g)=120 degrees C). The recrystallizable amorphous phase is invariably obtained by the melt of the polymorph TRE-alpha, while other procedures always give an amorphous phase that is unable to crystallize above T(g). The existence of two different categories is analyzed in terms of the transformation paths and the hypothesis that the systems may exhibit different molecular mobilities.

  10. Amorphous diamond films

    DOEpatents

    Falabella, S.

    1998-06-09

    Amorphous diamond films having a significant reduction in intrinsic stress are prepared by biasing a substrate to be coated and depositing carbon ions thereon under controlled temperature conditions. 1 fig.

  11. Amorphous metal alloy

    DOEpatents

    Wang, R.; Merz, M.D.

    1980-04-09

    Amorphous metal alloys of the iron-chromium and nickel-chromium type have excellent corrosion resistance and high temperature stability and are suitable for use as a protective coating on less corrosion resistant substrates. The alloys are stabilized in the amorphous state by one or more elements of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, and tungsten. The alloy is preferably prepared by sputter deposition.

  12. Formation of amorphous materials

    DOEpatents

    Johnson, William L.; Schwarz, Ricardo B.

    1986-01-01

    Metastable amorphous or fine crystalline materials are formed by solid state reactions by diffusion of a metallic component into a solid compound or by diffusion of a gas into an intermetallic compound. The invention can be practiced on layers of metals deposited on an amorphous substrate or by intermixing powders with nucleating seed granules. All that is required is that the diffusion of the first component into the second component be much faster than the self-diffusion of the first component. The method is practiced at a temperature below the temperature at which the amorphous phase transforms into one or more crystalline phases and near or below the temperature at which the ratio of the rate of diffusion of the first component to the rate of self-diffusion is at least 10.sup.4. This anomalous diffusion criteria is found in many binary, tertiary and higher ordered systems of alloys and appears to be found in all alloy systems that form amorphous materials by rapid quenching. The method of the invention can totally convert much larger dimensional materials to amorphous materials in practical periods of several hours or less.

  13. Structural Amorphous Steels

    NASA Astrophysics Data System (ADS)

    Lu, Z. P.; Liu, C. T.; Thompson, J. R.; Porter, W. D.

    2004-06-01

    Recent advancement in bulk metallic glasses, whose properties are usually superior to their crystalline counterparts, has stimulated great interest in fabricating bulk amorphous steels. While a great deal of effort has been devoted to this field, the fabrication of structural amorphous steels with large cross sections has remained an alchemist’s dream because of the limited glass-forming ability (GFA) of these materials. Here we report the discovery of structural amorphous steels that can be cast into glasses with large cross-section sizes using conventional drop-casting methods. These new steels showed interesting physical, magnetic, and mechanical properties, along with high thermal stability. The underlying mechanisms for the superior GFA of these materials are discussed.

  14. Amorphous semiconductor solar cell

    DOEpatents

    Dalal, Vikram L.

    1981-01-01

    A solar cell comprising a back electrical contact, amorphous silicon semiconductor base and junction layers and a top electrical contact includes in its manufacture the step of heat treating the physical junction between the base layer and junction layer to diffuse the dopant species at the physical junction into the base layer.

  15. Amorphous silicon photovoltaic devices

    DOEpatents

    Carlson, David E.; Lin, Guang H.; Ganguly, Gautam

    2004-08-31

    This invention is a photovoltaic device comprising an intrinsic or i-layer of amorphous silicon and where the photovoltaic device is more efficient at converting light energy to electric energy at high operating temperatures than at low operating temperatures. The photovoltaic devices of this invention are suitable for use in high temperature operating environments.

  16. Comparison of high temperature, high frequency core loss and dynamic B-H loops of two 50 Ni-Fe crystalline alloys and an iron-based amorphous alloy

    NASA Technical Reports Server (NTRS)

    Wieserman, W. R.; Schwarze, G. E.; Niedra, J. M.

    1991-01-01

    The availability of experimental data that characterizes the performance of soft magnetic materials for the combined conditions of high temperature and high frequency is almost nonexistent. An experimental investigation was conducted over the temperature range of 23 to 300 C and frequency range of 1 to 50 kHz to determine the effects of temperature and frequency on the core loss and dynamic B-H loops of three different soft magnetic materials; and oriented grain 50Ni-50Fe alloy, a nonoriented grain 50Ni-Fe alloy, and an iron based amorphous material (Metglas 2605SC). A comparison of these materials shows that the nonoriented grain 50Ni-50Fe alloy tends to have either the lowest or next lowest core loss for all temperatures and frequencies investigated.

  17. Amorphous silicon radiation detectors

    DOEpatents

    Street, R.A.; Perez-Mendez, V.; Kaplan, S.N.

    1992-11-17

    Hydrogenated amorphous silicon radiation detector devices having enhanced signal are disclosed. Specifically provided are transversely oriented electrode layers and layered detector configurations of amorphous silicon, the structure of which allow high electric fields upon application of a bias thereby beneficially resulting in a reduction in noise from contact injection and an increase in signal including avalanche multiplication and gain of the signal produced by incoming high energy radiation. These enhanced radiation sensitive devices can be used as measuring and detection means for visible light, low energy photons and high energy ionizing particles such as electrons, x-rays, alpha particles, beta particles and gamma radiation. Particular utility of the device is disclosed for precision powder crystallography and biological identification. 13 figs.

  18. Amorphous silicon radiation detectors

    DOEpatents

    Street, Robert A.; Perez-Mendez, Victor; Kaplan, Selig N.

    1992-01-01

    Hydrogenated amorphous silicon radiation detector devices having enhanced signal are disclosed. Specifically provided are transversely oriented electrode layers and layered detector configurations of amorphous silicon, the structure of which allow high electric fields upon application of a bias thereby beneficially resulting in a reduction in noise from contact injection and an increase in signal including avalanche multiplication and gain of the signal produced by incoming high energy radiation. These enhanced radiation sensitive devices can be used as measuring and detection means for visible light, low energy photons and high energy ionizing particles such as electrons, x-rays, alpha particles, beta particles and gamma radiation. Particular utility of the device is disclosed for precision powder crystallography and biological identification.

  19. Amorphous to amorphous transition in particle rafts

    NASA Astrophysics Data System (ADS)

    Varshney, Atul; Sane, A.; Ghosh, Shankar; Bhattacharya, S.

    2012-09-01

    Space-filling assemblies of athermal hydrophobic particles floating at an air-water interface, called particle rafts, are shown to undergo an unusual phase transition between two amorphous states, i.e., a low density “less-rigid” state and a high density “more-rigid” state, as a function of particulate number density (Φ). The former is shown to be a capillary bridged solid and the latter is shown to be a frictionally coupled one. Simultaneous studies involving direct imaging as well as measuring its mechanical response to longitudinal and shear stresses show that the transition is marked by a subtle structural anomaly and a weakening of the shear response. The structural anomaly is identified from the variation of the mean coordination number, mean area of the Voronoi cells, and spatial profile of the displacement field with Φ. The weakened shear response is related to local plastic instabilities caused by the depinning of the contact line of the underlying fluid on the rough surfaces of the particles.

  20. Amorphous to amorphous transition in particle rafts.

    PubMed

    Varshney, Atul; Sane, A; Ghosh, Shankar; Bhattacharya, S

    2012-09-01

    Space-filling assemblies of athermal hydrophobic particles floating at an air-water interface, called particle rafts, are shown to undergo an unusual phase transition between two amorphous states, i.e., a low density "less-rigid" state and a high density "more-rigid" state, as a function of particulate number density (Φ). The former is shown to be a capillary bridged solid and the latter is shown to be a frictionally coupled one. Simultaneous studies involving direct imaging as well as measuring its mechanical response to longitudinal and shear stresses show that the transition is marked by a subtle structural anomaly and a weakening of the shear response. The structural anomaly is identified from the variation of the mean coordination number, mean area of the Voronoi cells, and spatial profile of the displacement field with Φ. The weakened shear response is related to local plastic instabilities caused by the depinning of the contact line of the underlying fluid on the rough surfaces of the particles.

  1. 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.

  2. Amorphous silicon ionizing particle detectors

    DOEpatents

    Street, R.A.; Mendez, V.P.; Kaplan, S.N.

    1988-11-15

    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. 15 figs.

  3. Compensated amorphous silicon solar cell

    DOEpatents

    Devaud, Genevieve

    1983-01-01

    An amorphous silicon solar cell including an electrically conductive substrate, a layer of glow discharge deposited hydrogenated amorphous silicon over said substrate and having regions of differing conductivity with at least one region of intrinsic hydrogenated amorphous silicon. The layer of hydrogenated amorphous silicon has opposed first and second major surfaces where the first major surface contacts the electrically conductive substrate and an electrode for electrically contacting the second major surface. The intrinsic hydrogenated amorphous silicon region is deposited in a glow discharge with an atmosphere which includes not less than about 0.02 atom percent mono-atomic boron. An improved N.I.P. solar cell is disclosed using a BF.sub.3 doped intrinsic layer.

  4. Bulk amorphous materials

    SciTech Connect

    Schwarz, R.B.; Archuleta, J.I.; Sickafus, K.E.

    1998-12-01

    This is the final report for a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The objective of this work was to develop the competency for the synthesis of novel bulk amorphous alloys. The authors researched their synthesis methods and alloy properties, including thermal stability, mechanical, and transport properties. The project also addressed the development of vanadium-spinel alloys for structural applications in hostile environments, the measurement of elastic constants and thermal expansion in single-crystal TiAl from 300 to 750 K, the measurement of elastic constants in gallium nitride, and a study of the shock-induced martensitic transformations in NiTi alloys.

  5. Processing of amorphous PEEK and amorphous PEEK based composites

    SciTech Connect

    Kenny, J.; D'amore, A.; Nicolais, L.; Iannone, M.; Scatteia, B.; Aeritalia, S.p.A., Naples )

    1989-08-01

    An analysis of the crystallization behavior of amorphous PEEK, its carbon fiber composite, and its relationships with dynamic-mechanical properties of the system measured during and after processing is presented. The effect of the processing conditions, time and temperature, on the quality and on the amount of the crystallinity developed during cold crystallization has been investigated in order to evaluate the processability window of amorphous PEEK and amorphous PEEK based composite above the glass transition temperature and below the melting point. Also, the anomalous behavior of the amorphous matrix, crystallized at low temperatures, has been studied. Multiple melting peaks and changes of the glass transition during crystallization are explained in terms of crystalline morphology and molecular mobility. 20 refs.

  6. Apatite Formation from Amorphous Calcium Phosphate and Mixed Amorphous Calcium Phosphate/Amorphous Calcium Carbonate.

    PubMed

    Ibsen, Casper J S; Chernyshov, Dmitry; Birkedal, Henrik

    2016-08-22

    Crystallization from amorphous phases is an emerging pathway for making advanced materials. Biology has made use of amorphous precursor phases for eons and used them to produce structures with remarkable properties. Herein, we show how the design of the amorphous phase greatly influences the nanocrystals formed therefrom. We investigate the transformation of mixed amorphous calcium phosphate/amorphous calcium carbonate phases into bone-like nanocrystalline apatite using in situ synchrotron X-ray diffraction and IR spectroscopy. The speciation of phosphate was controlled by pH to favor HPO4 (2-) . In a carbonate free system, the reaction produces anisotropic apatite crystallites with large aspect ratios. The first formed crystallites are highly calcium deficient and hydrogen phosphate rich, consistent with thin octacalcium phosphate (OCP)-like needles. During growth, the crystallites become increasingly stoichiometric, which indicates that the crystallites grow through addition of near-stoichiometric apatite to the OCP-like initial crystals through a process that involves either crystallite fusion/aggregation or Ostwald ripening. The mixed amorphous phases were found to be more stable against phase transformations, hence, the crystallization was inhibited. The resulting crystallites were smaller and less anisotropic. This is rationalized by the idea that a local phosphate-depletion zone formed around the growing crystal until it was surrounded by amorphous calcium carbonate, which stopped the crystallization. PMID:27460160

  7. Fabrication of amorphous diamond films

    DOEpatents

    Falabella, S.

    1995-12-12

    Amorphous diamond films having a significant reduction in intrinsic stress are prepared by biasing a substrate to be coated and depositing carbon ions thereon under controlled temperature conditions. 1 fig.

  8. Amorphous metal alloy and composite

    DOEpatents

    Wang, Rong; Merz, Martin D.

    1985-01-01

    Amorphous metal alloys of the iron-chromium and nickel-chromium type have excellent corrosion resistance and high temperature stability and are suitable for use as a protective coating on less corrosion resistant substrates. The alloys are stabilized in the amorphous state by one or more elements of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, and tungsten. The alloy is preferably prepared by sputter deposition.

  9. Cantilever detected ferromagnetic resonance in thin Fe50Ni50, Co2FeAl0.5Si0.5 and Sr2FeMoO6 films using a double modulation technique.

    PubMed

    Alfonsov, Alexey; Ohmichi, Eiji; Leksin, Pavel; Omar, Ahmad; Wang, Hailong; Wurmehl, Sabine; Yang, Fengyuan; Ohta, Hitoshi

    2016-09-01

    In this work we introduce a new method, which employs commercial piezo-cantilevers, for a ferromagnetic resonance (FMR) detection from thin, nm-size, films. Our setup has an option to rotate the sample in the magnetic field and it operates up to the high microwave frequencies of 160GHz. Using our cantilever based FMR spectrometer we have investigated a set of samples, namely quasi-bulk and 84nm film Co2FeAl0.5Si0.5 samples, 16nm Fe50Ni50 film and 150nm Sr2FeMoO6 film. Low frequency and room temperature test of our setup using 84nm Co2FeAl0.5Si0.5 film yielded a result identical to a standard X-Band spectrometer, namely a single line with quite small linewidth. Our measurements at low temperatures and high frequencies revealed a quite strong FMR response detected in all samples. The FMR spectra share common features, such as the emergence of the second line with an opposite angular dependence, and a drastic increase of the linewidths with increasing microwave frequency. We believe that these findings are results of the complicated dynamics of the magnetization at low temperatures and high frequencies, which we were able to probe using our cantilever based FMR setup. PMID:27498338

  10. Cantilever detected ferromagnetic resonance in thin Fe50Ni50, Co2FeAl0.5Si0.5 and Sr2FeMoO6 films using a double modulation technique

    NASA Astrophysics Data System (ADS)

    Alfonsov, Alexey; Ohmichi, Eiji; Leksin, Pavel; Omar, Ahmad; Wang, Hailong; Wurmehl, Sabine; Yang, Fengyuan; Ohta, Hitoshi

    2016-09-01

    In this work we introduce a new method, which employs commercial piezo-cantilevers, for a ferromagnetic resonance (FMR) detection from thin, nm-size, films. Our setup has an option to rotate the sample in the magnetic field and it operates up to the high microwave frequencies of 160 GHz. Using our cantilever based FMR spectrometer we have investigated a set of samples, namely quasi-bulk and 84 nm film Co2FeAl0.5Si0.5 samples, 16 nm Fe50Ni50 film and 150 nm Sr2FeMoO6 film. Low frequency and room temperature test of our setup using 84 nm Co2FeAl0.5Si0.5 film yielded a result identical to a standard X-Band spectrometer, namely a single line with quite small linewidth. Our measurements at low temperatures and high frequencies revealed a quite strong FMR response detected in all samples. The FMR spectra share common features, such as the emergence of the second line with an opposite angular dependence, and a drastic increase of the linewidths with increasing microwave frequency. We believe that these findings are results of the complicated dynamics of the magnetization at low temperatures and high frequencies, which we were able to probe using our cantilever based FMR setup.

  11. Comparing magnetostructural transitions in Ni50Mn18.75Cu6.25Ga25 and Ni49.80Mn34.66In15.54 Heusler alloys

    NASA Astrophysics Data System (ADS)

    Dubenko, Igor; Granovsky, Alexander; Lahderanta, Erkki; Kashirin, Maxim; Makagonov, Vladimir; Aryal, Anil; Quetz, Abdiel; Pandey, Sudip; Rodionov, Igor; Samanta, Tapas; Stadler, Shane; Mazumdar, Dipanjan; Ali, Naushad

    2016-03-01

    The crystal structure, magnetic and transport properties, including resistivity and thermopower, of Ni50Mn18.75Cu6.25Ga25 and Ni49.80Mn34.66In15.54 Heusler alloys were studied in the (10-400) K temperature interval. We show that their physical properties are remarkably different, thereby pointing to different origin of their magnetostructural transition (MST). A Seebeck coefficient (S) was found to pass minimum of about -20 μV/K in respect of temperature for both compounds. It was shown that MST observed for both compounds results in jump-like changes in S for Ga-based compound and jump in resistivity of about 20 and 200 μΩ cm for Ga and In -based compounds, respectively. The combined analyzes of the present results with that from literature show that the density of states at the Fermi level does not change strongly at the MST in the case of Ni-Mn-In alloys as compared to that of Ni-Mn-Ga.

  12. Nanostructures having crystalline and amorphous phases

    DOEpatents

    Mao, Samuel S; Chen, Xiaobo

    2015-04-28

    The present invention includes a nanostructure, a method of making thereof, and a method of photocatalysis. In one embodiment, the nanostructure includes a crystalline phase and an amorphous phase in contact with the crystalline phase. Each of the crystalline and amorphous phases has at least one dimension on a nanometer scale. In another embodiment, the nanostructure includes a nanoparticle comprising a crystalline phase and an amorphous phase. The amorphous phase is in a selected amount. In another embodiment, the nanostructure includes crystalline titanium dioxide and amorphous titanium dioxide in contact with the crystalline titanium dioxide. Each of the crystalline and amorphous titanium dioxide has at least one dimension on a nanometer scale.

  13. Amorphous-diamond electron emitter

    DOEpatents

    Falabella, Steven

    2001-01-01

    An electron emitter comprising a textured silicon wafer overcoated with a thin (200 .ANG.) layer of nitrogen-doped, amorphous-diamond (a:D-N), which lowers the field below 20 volts/micrometer have been demonstrated using this emitter compared to uncoated or diamond coated emitters wherein the emission is at fields of nearly 60 volts/micrometer. The silicon/nitrogen-doped, amorphous-diamond (Si/a:D-N) emitter may be produced by overcoating a textured silicon wafer with amorphous-diamond (a:D) in a nitrogen atmosphere using a filtered cathodic-arc system. The enhanced performance of the Si/a:D-N emitter lowers the voltages required to the point where field-emission displays are practical. Thus, this emitter can be used, for example, in flat-panel emission displays (FEDs), and cold-cathode vacuum electronics.

  14. Annealing studies of amorphous alloys

    SciTech Connect

    Wiley, J.D.; Perepezko, J.H.; Nordman, J.E.

    1983-04-01

    Amorphous films of the alloys Ni-Nb, Ni-Mo, Mo-Si, and W-Si were sputter deposited on single-crystal semiconductor substrates. One-hour crystallization temperatures of the films were determined to within +-25/sup 0/C by annealing and x-ray diffraction measurements. Interdiffusion between Au or Cu overlayers and the amorphous films were studied by annealing combined with Auger Electron Spectroscopy (AES) profiling, and by Rutherford Backscatter (RBS) analysis. Supplementary measurements used to study structural relaxation and crystallization included resistivity as a function of temperature; DTA and DSC; and electron microscopy.

  15. Imprinting bulk amorphous alloy at room temperature

    PubMed Central

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; Lograsso, Thomas A.; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-01-01

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. Our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment. PMID:26563908

  16. Imprinting bulk amorphous alloy at room temperature.

    PubMed

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T; Lograsso, Thomas A; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-01-01

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. Our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment. PMID:26563908

  17. Imprinting bulk amorphous alloy at room temperature

    NASA Astrophysics Data System (ADS)

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; Lograsso, Thomas A.; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-11-01

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. Our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment.

  18. Imprinting bulk amorphous alloy at room temperature

    SciTech Connect

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; Lograsso, Thomas A.; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-11-13

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. In conclusion, our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment.

  19. Amorphous rare earth magnet powders

    SciTech Connect

    Sellers, C.H.; Branagan, D.J.; Hyde, T.A.; Lewis, L.H.; Panchanathan, V.

    1996-08-01

    Gas atomization (GA) processing does not generally have a high enough cooling rate to produce the initial amorphous microstructure needed to obtain optimal magnetic properties in RE{sub 2}Fe{sub 14}B alloys. Phase separation and an underquenched microstructure result from detrimental {alpha}-Fe precipitation, and the resulting magnetic domain structure is very coarse. Additionally, there is a dramatic dependence of the magnetic properties on the cooling rate (and therefore the particle size) and the powders can be sensitive to environmental degradation. Alloy compositions designed just for GA (as opposed to melt spinning) are necessary to produce an amorphous structure that can be crystallized to result in a fine structure with magnetic properties which are independent of particle size. The addition of titanium and carbon to the melt has been found to change the solidification process sufficiently to result in an ``overquenched`` state in which most of the powder size fractions have an amorphous component. Crystallization with a brief heat treatment produces a structure which has improved magnetic properties, in part due to the ability to use compositions with higher Fe contents without {alpha}-Fe precipitation. Results from magnetometry, magnetic force microscopy, and x-ray analyses will be used to contrast the microstructure, domain structure, and magnetic properties of this new generation of amorphous powders with their multiphase predecessors.

  20. Amorphous titanium-oxide supercapacitors

    PubMed Central

    Fukuhara, Mikio; Kuroda, Tomoyuki; Hasegawa, Fumihiko

    2016-01-01

    The electric capacitance of an amorphous TiO2-x surface increases proportionally to the negative sixth power of the convex diameter d. This occurs because of the van der Waals attraction on the amorphous surface of up to 7 mF/cm2, accompanied by extreme enhanced electron trapping resulting from both the quantum-size effect and an offset effect from positive charges at oxygen-vacancy sites. Here we show that a supercapacitor, constructed with a distributed constant-equipment circuit of large resistance and small capacitance on the amorphous TiO2-x surface, illuminated a red LED for 37 ms after it was charged with 1 mA at 10 V. The fabricated device showed no dielectric breakdown up to 1,100 V. Based on this approach, further advances in the development of amorphous titanium-dioxide supercapacitors might be attained by integrating oxide ribbons with a micro-electro mechanical system. PMID:27767103

  1. Tandem junction amorphous silicon solar cells

    DOEpatents

    Hanak, Joseph J.

    1981-01-01

    An amorphous silicon solar cell has an active body with two or a series of layers of hydrogenated amorphous silicon arranged in a tandem stacked configuration with one optical path and electrically interconnected by a tunnel junction. The layers of hydrogenated amorphous silicon arranged in tandem configuration can have the same bandgap or differing bandgaps.

  2. Crystallization study of amorphous sputtered NiTi bi-layer thin film

    SciTech Connect

    Mohri, Maryam; Nili-Ahmadabadi, Mahmoud; Chakravadhanula, Venkata Sai Kiran

    2015-05-15

    The crystallization of Ni-rich/NiTiCu bi-layer thin film deposited by magnetron sputtering from two separate alloy targets was investigated. To achieve the shape memory effect, the NiTi thin films deposited at room temperature with amorphous structure were annealed at 773 K for 15, 30, and 60 min for crystallization. Characterization of the films was carried out by differential scanning calorimetry to indicate the crystallization temperature, grazing incidence X-ray diffraction to identify the phase structures, atomic force microscopy to evaluate surface morphology, scanning transmission electron microscopy to study the cross section of the thin films. The results show that the structure of the annealed thin films strongly depends on the temperature and time of the annealing. Crystalline grains nucleated first at the surface and then grew inward to form columnar grains. Furthermore, the crystallization behavior was markedly affected by composition variations. - Highlights: • A developed bi-layer Ni45TiCu5/Ni50.8Ti was deposited on Si substrate and crystallized. • During crystallization, The Ni{sub 45}TiCu{sub 5} layer is thermally less stable than the Ni-rich layer. • The activation energy is 302 and 464 kJ/mol for Cu-rich and Ni-rich layer in bi-layer, respectively.

  3. Uranium incorporation into amorphous silica.

    PubMed

    Massey, Michael S; Lezama-Pacheco, Juan S; Nelson, Joey M; Fendorf, Scott; Maher, Kate

    2014-01-01

    High concentrations of uranium are commonly observed in naturally occurring amorphous silica (including opal) deposits, suggesting that incorporation of U into amorphous silica may represent a natural attenuation mechanism and promising strategy for U remediation. However, the stability of uranium in opaline silicates, determined in part by the binding mechanism for U, is an important factor in its long-term fate. U may bind directly to the opaline silicate matrix, or to materials such as iron (hydr)oxides that are subsequently occluded within the opal. Here, we examine the coordination environment of U within opaline silica to elucidate incorporation mechanisms. Precipitates (with and without ferrihydrite inclusions) were synthesized from U-bearing sodium metasilicate solutions, buffered at pH ∼ 5.6. Natural and synthetic solids were analyzed with X-ray absorption spectroscopy and a suite of other techniques. In synthetic amorphous silica, U was coordinated by silicate in a double corner-sharing coordination geometry (Si at ∼ 3.8-3.9 Å) and a small amount of uranyl and silicate in a bidentate, mononuclear (edge-sharing) coordination (Si at ∼ 3.1-3.2 Å, U at ∼ 3.8-3.9 Å). In iron-bearing synthetic solids, U was adsorbed to iron (hydr)oxide, but the coordination environment also contained silicate in both edge-sharing and corner-sharing coordination. Uranium local coordination in synthetic solids is similar to that of natural U-bearing opals that retain U for millions of years. The stability and extent of U incorporation into opaline and amorphous silica represents a long-term repository for U that may provide an alternative strategy for remediation of U contamination. PMID:24984107

  4. Stability study of amorphous valdecoxib.

    PubMed

    Ambike, Anshuman A; Mahadik, K R; Paradkar, Anant

    2004-09-10

    Formulation of poorly water-soluble drugs in the most stable dosage form for oral delivery perhaps presents the greatest challenge to pharmaceutical industry. Physical transformation of drug substance into its more soluble but metastable amorphous form is one of the approaches for improving dissolution rate of such drugs. The present study utilizes technique of spray drying for preparation of solid dispersions (SDs) and includes stability study of the same. Valdecoxib (VLD), a prototype of poorly water-soluble drugs, has been the drug of choice. The hydrophilic carriers selected were polyvinylpyrrolidone K30 (PVP) and hydroxypropylcellulose (HPC). SDs and pure VLD in the form of spray dried powder (SDVLD) in comparison with pure drug and corresponding physical mixtures (PMs) were initially characterized and then subjected to stability testing at ambient temperature and relative humidity up to 3 months. During initial characterization, increase in saturation solubility and dissolution rate was observed in all samples. DSC and XRPD studies of SDVLD and SDs suggested generation of amorphous form of drug. IR spectroscopy revealed presence of hydrogen bonding in SDs. During stability testing, there was gradual decrease in saturation solubility and dissolution rate of SDs, over the period of 3 months. While, saturation solubility of SDVLD dropped drastically within 15 days and was almost comparable with pure VLD. SD PVP retained the amorphous form of drug throughout stability period, whereas SD HPC and SDVLD presented incidence of crystallinity after 1 month and 15 days, respectively. This was justified by enthalpy relaxation studies in which, amorphous VLD showed considerable relaxation of enthalpy at Tg, while it was totally suppressed in SD PVP and partly in SD HPC. The study thus definitely reveals tremendous potential of solid dispersions of valdecoxib with PVP, from stability point of view.

  5. Visual Observations of the Amorphous-Amorphous Transition in H2O Under Pressure.

    PubMed

    Mishima, O; Takemura, K; Aoki, K

    1991-10-18

    The vapor-deposited low-density amorphous phase of H(2)O was directly compressed at 77 kelvin with a diamond-anvil cell, and the boundary between the low-density amorphous phase and the high-density amorphous phase was observed while the sample was warmed under compression. The transition from the low-density amorphous phase to the high-density amorphous phase was distinct and reversible in an apparently narrow pressure range at approximately 130 to approximately 150 kelvin, which provided experimental evidence for polymorphism in amorphous H(2)O. PMID:17742228

  6. Narrow band gap amorphous silicon semiconductors

    DOEpatents

    Madan, A.; Mahan, A.H.

    1985-01-10

    Disclosed is a narrow band gap amorphous silicon semiconductor comprising an alloy of amorphous silicon and a band gap narrowing element selected from the group consisting of Sn, Ge, and Pb, with an electron donor dopant selected from the group consisting of P, As, Sb, Bi and N. The process for producing the narrow band gap amorphous silicon semiconductor comprises the steps of forming an alloy comprising amorphous silicon and at least one of the aforesaid band gap narrowing elements in amount sufficient to narrow the band gap of the silicon semiconductor alloy below that of amorphous silicon, and also utilizing sufficient amounts of the aforesaid electron donor dopant to maintain the amorphous silicon alloy as an n-type semiconductor.

  7. Amorphous silicon solar cell allowing infrared transmission

    DOEpatents

    Carlson, David E.

    1979-01-01

    An amorphous silicon solar cell with a layer of high index of refraction material or a series of layers having high and low indices of refraction material deposited upon a transparent substrate to reflect light of energies greater than the bandgap energy of the amorphous silicon back into the solar cell and transmit solar radiation having an energy less than the bandgap energy of the amorphous silicon.

  8. Preparation of amorphous sulfide sieves

    DOEpatents

    Siadati, Mohammad H.; Alonso, Gabriel; Chianelli, Russell R.

    2006-11-07

    The present invention involves methods and compositions for synthesizing catalysts/porous materials. In some embodiments, the resulting materials are amorphous sulfide sieves that can be mass-produced for a variety of uses. In some embodiments, methods of the invention concern any suitable precursor (such as thiomolybdate salt) that is exposed to a high pressure pre-compaction, if need be. For instance, in some cases the final bulk shape (but highly porous) may be same as the original bulk shape. The compacted/uncompacted precursor is then subjected to an open-flow hot isostatic pressing, which causes the precursor to decompose and convert to a highly porous material/catalyst.

  9. Is Mg-stabilized amorphous calcium carbonate a homogeneous mixture of amorphous magnesium carbonate and amorphous calcium carbonate?

    PubMed

    Yang, Sheng-Yu; Chang, Hsun-Hui; Lin, Cang-Jie; Huang, Shing-Jong; Chan, Jerry C C

    2016-10-01

    We find two types of carbonate ions in Mg stabilized amorphous calcium carbonate (Mg-ACC), whose short-range orders are identical to those of ACC and amorphous magnesium carbonate (AMC). Mg-ACC comprises a homogeneous mixture of the nano-clusters of ACC and AMC. Their relative amount varies systematically at different pH. PMID:27524162

  10. New bulk amorphous magnetic materials

    NASA Astrophysics Data System (ADS)

    Chiriac, H.; Lupu, N.

    2001-06-01

    The relationship between structure and magnetic properties of the melt-spun ribbons with thicknesses up to 200 μm and rods having up to 3 mm diameter prepared by mould casting and suction casting techniques, of nominal compositions Fe 56Co 7Ni 7Zr 6M 1.5Nb 2.5B 20 (M=Zr, Ti, Ta or Mo) and Nd 50Fe 40Si 10- xAl x was investigated. Saturation magnetisations up to 1.1 T, coercive fields of about 5 A/m, magnetic permeabilities of 25 000-30 000 in the as-cast state were measured for the Fe-based amorphous alloys. The large values over 200 kA/m of the intrinsic coercive field at room temperature and over 600 kA/m at 200 K measured in low magnetic fields for the Nd-Fe-based “X-ray amorphous” alloys, and its dependence on temperature and cooling rate are ascribed to the existence of very small ferromagnetic clusters embedded in an Nd-rich matrix. The thermal treatments applied to the amorphous samples below the crystallisation temperature cause an improvement in the magnetic properties as a consequence of structural relaxation.

  11. Laser surface treatment of amorphous metals

    NASA Astrophysics Data System (ADS)

    Katakam, Shravana K.

    Amorphous materials are used as soft magnetic materials and also as surface coatings to improve the surface properties. Furthermore, the nanocrystalline materials derived from their amorphous precursors show superior soft magnetic properties than amorphous counter parts for transformer core applications. In the present work, laser based processing of amorphous materials will be presented. Conventionally, the nanocrystalline materials are synthesized by furnace heat treatment of amorphous precursors. Fe-based amorphous/nanocrystalline materials due to their low cost and superior magnetic properties are the most widely used soft magnetic materials. However, achieving nanocrystalline microstructure in Fe-Si-B ternary system becomes very difficult owing its rapid growth rate at higher temperatures and sluggish diffusion at low temperature annealing. Hence, nanocrystallization in this system is achieved by using alloying additions (Cu and Nb) in the ternary Fe-Si-B system. Thus, increasing the cost and also resulting in reduction of saturation magnetization. laser processing technique is used to achieve extremely fine nanocrystalline microstructure in Fe-Si-B amorphous precursor. Microstructure-magnetic Property-laser processing co-relationship has been established for Fe-Si-B ternary system using analytical techniques. Laser processing improved the magnetic properties with significant increase in saturation magnetization and near zero coercivity values. Amorphous materials exhibit excellent corrosion resistance by virtue of their atomic structure. Fe-based amorphous materials are economical and due to their ease of processing are of potential interest to synthesize as coatings materials for wear and corrosion resistance applications. Fe-Cr-Mo-Y-C-B amorphous system was used to develop thick coatings on 4130 Steel substrate and the corrosion resistance of the amorphous coatings was improved. It is also shown that the mode of corrosion depends on the laser processing

  12. Fluorination of amorphous thin-film materials with xenon fluoride

    DOEpatents

    Weil, Raoul B.

    1988-01-01

    A method is disclosed for producing fluorine-containing amorphous semiconductor material, preferably comprising amorphous silicon. The method includes depositing amorphous thin-film material onto a substrate while introducing xenon fluoride during the film deposition process.

  13. Fluorination of amorphous thin-film materials with xenon fluoride

    DOEpatents

    Weil, R.B.

    1987-05-01

    A method is disclosed for producing fluorine-containing amorphous semiconductor material, preferably comprising amorphous silicon. The method includes depositing amorphous thin-film material onto a substrate while introducing xenon fluoride during the film deposition process.

  14. Method of making amorphous metal composites

    DOEpatents

    Byrne, Martin A.; Lupinski, John H.

    1982-01-01

    The process comprises placing an amorphous metal in particulate form and a low molecular weight (e.g., 1000-5000) thermosetting polymer binder powder into a container, mixing these materials, and applying heat and pressure to convert the mixture into an amorphous metal composite.

  15. Electron tunnelling into amorphous germanium and silicon.

    NASA Technical Reports Server (NTRS)

    Smith, C. W.; Clark, A. H.

    1972-01-01

    Measurements of tunnel conductance versus bias, capacitance versus bias, and internal photoemission were made in the systems aluminum-oxide-amorphous germanium and aluminium-oxide-amorphous silicon. A function was extracted which expresses the deviation of these systems from the aluminium-oxide-aluminium system.

  16. Electron beam recrystallization of amorphous semiconductor materials

    NASA Technical Reports Server (NTRS)

    Evans, J. C., Jr.

    1968-01-01

    Nucleation and growth of crystalline films of silicon, germanium, and cadmium sulfide on substrates of plastic and glass were investigated. Amorphous films of germanium, silicon, and cadmium sulfide on amorphous substrates of glass and plastic were converted to the crystalline condition by electron bombardment.

  17. Imprinting bulk amorphous alloy at room temperature

    DOE PAGES

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; Lograsso, Thomas A.; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-11-13

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the abilitymore » of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. In conclusion, our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment.« less

  18. Compensated amorphous-silicon solar cell

    DOEpatents

    Devaud, G.

    1982-06-21

    An amorphous silicon solar cell including an electrically conductive substrate, a layer of glow discharge deposited hydrogenated amorphous silicon having regions of differing conductivity with at least one region of intrinsic hydrogenated amorphous silicon. The layer of hydrogenated amorphous silicon has opposed first and second major surfaces where the first major surface contacts the elecrically conductive substrate and an electrode for electrically contacting the second major surface. The intrinsic hydrogenated amorphous silicon region is deposited in a glow discharge with an atmosphere which includes not less than about 0.02 atom percent mono-atomic boron. An improved N.I.P. solar cell is disclosed using a BF/sub 3/ doped intrinsic layer.

  19. Structure, thermodynamics, and crystallization of amorphous hafnia

    SciTech Connect

    Luo, Xuhui; Demkov, Alexander A.

    2015-09-28

    We investigate theoretically amorphous hafnia using the first principles melt and quench method. We identify two types of amorphous structures of hafnia. Type I and type II are related to tetragonal and monoclinic hafnia, respectively. We find type II structure to show stronger disorder than type I. Using the phonon density of states, we calculate the specific heat capacity for type II amorphous hafnia. Using the nudged elastic band method, we show that the averaged transition barrier between the type II amorphous hafnia and monoclinic phase is approximately 0.09 eV/HfO{sub 2}. The crystallization temperature is estimated to be 421 K. The calculations suggest an explanation for the low thermal stability of amorphous hafnia.

  20. Solid-state diffusion in amorphous zirconolite

    SciTech Connect

    Yang, C.; Dove, M. T.; Trachenko, K.; Zarkadoula, E.; Todorov, I. T.; Geisler, T.; Brazhkin, V. V.

    2014-11-14

    We discuss how structural disorder and amorphization affect solid-state diffusion, and consider zirconolite as a currently important case study. By performing extensive molecular dynamics simulations, we disentangle the effects of amorphization and density, and show that a profound increase of solid-state diffusion takes place as a result of amorphization. Importantly, this can take place at the same density as in the crystal, representing an interesting general insight regarding solid-state diffusion. We find that decreasing the density in the amorphous system increases pre-factors of diffusion constants, but does not change the activation energy in the density range considered. We also find that atomic species in zirconolite are affected differently by amorphization and density change. Our microscopic insights are relevant for understanding how solid-state diffusion changes due to disorder and for building predictive models of operation of materials to be used to encapsulate nuclear waste.

  1. Solid-state diffusion in amorphous zirconolite

    NASA Astrophysics Data System (ADS)

    Yang, C.; Zarkadoula, E.; Dove, M. T.; Todorov, I. T.; Geisler, T.; Brazhkin, V. V.; Trachenko, K.

    2014-11-01

    We discuss how structural disorder and amorphization affect solid-state diffusion, and consider zirconolite as a currently important case study. By performing extensive molecular dynamics simulations, we disentangle the effects of amorphization and density, and show that a profound increase of solid-state diffusion takes place as a result of amorphization. Importantly, this can take place at the same density as in the crystal, representing an interesting general insight regarding solid-state diffusion. We find that decreasing the density in the amorphous system increases pre-factors of diffusion constants, but does not change the activation energy in the density range considered. We also find that atomic species in zirconolite are affected differently by amorphization and density change. Our microscopic insights are relevant for understanding how solid-state diffusion changes due to disorder and for building predictive models of operation of materials to be used to encapsulate nuclear waste.

  2. Neutron irradiation induced amorphization of silicon carbide

    SciTech Connect

    Snead, L.L.; Hay, J.C.

    1998-09-01

    This paper provides the first known observation of silicon carbide fully amorphized under neutron irradiation. Both high purity single crystal hcp and high purity, highly faulted (cubic) chemically vapor deposited (CVD) SiC were irradiated at approximately 60 C to a total fast neutron fluence of 2.6 {times} 10{sup 25} n/m{sup 2}. Amorphization was seen in both materials, as evidenced by TEM, electron diffraction, and x-ray diffraction techniques. Physical properties for the amorphized single crystal material are reported including large changes in density ({minus}10.8%), elastic modulus as measured using a nanoindentation technique ({minus}45%), hardness as measured by nanoindentation ({minus}45%), and standard Vickers hardness ({minus}24%). Similar property changes are observed for the critical temperature for amorphization at this neutron dose and flux, above which amorphization is not possible, is estimated to be greater than 130 C.

  3. Locomotion of Amorphous Surface Robots

    NASA Technical Reports Server (NTRS)

    Bradley, Arthur T. (Inventor)

    2016-01-01

    An amorphous robot includes a compartmented bladder containing fluid, a valve assembly, and an outer layer encapsulating the bladder and valve assembly. The valve assembly draws fluid from a compartment(s) and discharges the drawn fluid into a designated compartment to displace the designated compartment with respect to the surface. Another embodiment includes elements each having a variable property, an outer layer that encapsulates the elements, and a control unit. The control unit energizes a designated element to change its variable property, thereby moving the designated element. The elements may be electromagnetic spheres with a variable polarity or shape memory polymers with changing shape and/or size. Yet another embodiment includes an elongated flexible tube filled with ferrofluid, a moveable electromagnet, an actuator, and a control unit. The control unit energizes the electromagnet and moves the electromagnet via the actuator to magnetize the ferrofluid and lengthen the flexible tube.

  4. Biologically formed amorphous calcium carbonate.

    PubMed

    Weiner, Steve; Levi-Kalisman, Yael; Raz, Sefi; Addadi, Lia

    2003-01-01

    Many organisms from a wide variety of taxa produce amorphous calcium carbonate (ACC), despite the fact that it is inherently unstable and relatively soluble in its pure state. These properties also make it difficult to detect and characterize ACC. Raman spectroscopy is a particularly useful method for investigating ACC because the sample can be examined wet, and extended X-ray absorption fine structure (EXAFS) analysis can provide detailed information on the short-range order. Other methods for characterizing ACC include infrared spectroscopy, thermogravimetric analysis and differential thermal analysis (TGA and DTA), transmission electron microscopy (TEM), and electron and X-ray diffraction. Because of the difficulties involved, we suspect that ACC is far more widely distributed than is presently known, and a comparison of EXAFS spectra shows that different biogenic ACC phases have different short-range order structures. We also suspect that ACC fulfils many different functions, including as a transient precursor phase during the formation of crystalline calcium carbonate.

  5. Locomotion of Amorphous Surface Robots

    NASA Technical Reports Server (NTRS)

    Bradley, Arthur T. (Inventor)

    2014-01-01

    An amorphous robot includes a compartmented bladder containing fluid, a valve assembly, and an outer layer encapsulating the bladder and valve assembly. The valve assembly draws fluid from a compartment(s) and discharges the drawn fluid into a designated compartment to displace the designated compartment with respect to the surface. Another embodiment includes elements each having a variable property, an outer layer that encapsulates the elements, and a control unit. The control unit energizes a designated element to change its variable property, thereby moving the designated element. The elements may be electromagnetic spheres with a variable polarity or shape memory polymers with changing shape and/or size. Yet another embodiment includes an elongated flexible tube filled with ferrofluid, a moveable electromagnet, an actuator, and a control unit. The control unit energizes the electromagnet and moves the electromagnet via the actuator to magnetize the ferrofluid and lengthen the flexible tube.

  6. Quantification of surface amorphous content using dispersive surface energy: the concept of effective amorphous surface area.

    PubMed

    Brum, Jeffrey; Burnett, Daniel

    2011-09-01

    We investigate the use of dispersive surface energy in quantifying surface amorphous content, and the concept of effective amorphous surface area is introduced. An equation is introduced employing the linear combination of surface area normalized square root dispersive surface energy terms. This equation is effective in generating calibration curves when crystalline and amorphous references are used. Inverse gas chromatography is used to generate dispersive surface energy values. Two systems are investigated, and in both cases surface energy data collected for physical mixture samples comprised of amorphous and crystalline references fits the predicted response with good accuracy. Surface amorphous content of processed lactose samples is quantified using the calibration curve, and interpreted within the context of effective amorphous surface area. Data for bulk amorphous content is also utilized to generate a thorough picture of how disorder is distributed throughout the particle. An approach to quantifying surface amorphous content using dispersive surface energy is presented. Quantification is achieved by equating results to an effective amorphous surface area based on reference crystalline, and amorphous materials. PMID:21725707

  7. Observation of a rapid amorphization reaction

    SciTech Connect

    Hufnagel, T.C. ); Brennan, S. ); Payne, A.P.; Clemens, B.M. )

    1992-08-01

    We have observed a rapid amorphization reaction at ambient temperature in the Gd/Co system by employing grazing incidence x-ray scattering. We find that a 135 A crystalline Gd film is amporhized in less than 30 min by deposition of Co. We postulate that the rapidity of the reaction is due to surface diffusion of Co atoms after deposition to fast diffusion sites such as grain boundaries in the Gd film. Once the interfacial region has been amorphized these fast diffusion paths are sealed off from the surface, rapid diffusion of Co into the Gd crystalline layer is prevented, and the amorphization reaction stops.

  8. Pressure induced crystallization in amorphous silicon

    NASA Astrophysics Data System (ADS)

    Pandey, K. K.; Garg, Nandini; Shanavas, K. V.; Sharma, Surinder M.; Sikka, S. K.

    2011-06-01

    We have investigated the high pressure behavior of amorphous silicon (a-Si) using x-ray diffraction and Raman scattering techniques. Our experiments show that a-Si undergoes a polyamorphous transition from the low density amorphous to the high density amorphous phase, followed by pressure induced crystallization to the primitive hexagonal (ph) phase. On the release path, the sequence of observed phase transitions depends on whether the pressure is reduced slowly or rapidly. Using the results of our first principles calculations, pressure induced preferential crystallization to the ph phase is explained in terms of a thermodynamic model based on phenomenological random nucleation and the growth process.

  9. Selective laser sintering of amorphous metal powder

    NASA Astrophysics Data System (ADS)

    Fischer, P.; Blatter, A.; Romano, V.; Weber, H. P.

    2005-02-01

    For the first time, selective sintering of amorphous PtCuNiP powder with a pulsed Nd:YAG laser has been studied. Upon pulsed interaction, the grains melt only superficially to build necks between the grains. Depending on the laser parameters, the sintered material can be crystallized or retained amorphous. By contrast with crystalline powder, laser sintering of amorphous powder is achieved at substantially lower pulse energies due to its low melting point. The obtained results are compared with previous results from selective laser sintering of titanium powder.

  10. Method of producing hydrogenated amorphous silicon film

    DOEpatents

    Wiesmann, Harold J.

    1980-01-01

    This invention relates to hydrogenated amorphous silicon produced by thermally decomposing silane (SiH.sub.4) or other gases comprising H and Si, from a tungsten or carbon foil heated to a temperature of about 1400.degree.-1600.degree. C., in a vacuum of about 10.sup.-6 to 19.sup.-4 torr, to form a gaseous mixture of atomic hydrogen and atomic silicon, and depositing said gaseos mixture onto a substrate independent of and outside said source of thermal decomposition, to form hydrogenated amorphous silicon. The presence of an ammonia atmosphere in the vacuum chamber enhances the photoconductivity of the hydrogenated amorphous silicon film.

  11. Crystallization of amorphous solid films

    NASA Astrophysics Data System (ADS)

    Safarik, Douglas Joseph

    2003-06-01

    Below ˜130 K, H2O can exist for prolonged periods in a thermodynamically unstable, non-crystalline solid form known as amorphous solid water (ASW). When warmed to above 135 K, ASW crystallizes to the thermodynamically favored state, cubic ice I, on a laboratory time scale. Despite the relevance of ASW crystallization to a variety of scientific problems ranging from astrophysical phenomena to cryopreservation, the kinetics of this transformation are largely uncharacterized, and its mechanism is not fully understood. In the present work, the crystallization kinetics of vapor-deposited, nonporous ASW films less than one micron thick are investigated experimentally near 140 K. The amorphous to crystalline transition is characterized using a probe molecule, chlorodifluoromethane (CHF2Cl), whose adsorbed states and hence desorption kinetics are sensitive to the crystallinity of solid water surfaces. The transformation kinetics of very thick ASW films are found to be both independent of specimen size and consistent with simultaneous homogeneous nucleation and isotropic growth of crystalline ice grains. As the ASW film thickness is reduced from 385 nm to 55 nm, however, the rate of surface crystallization decelerates, in apparent conflict with a homogeneous nucleation and growth mechanism. In an attempt to explain this behavior, a geometrical model of phase transition kinetics at the surface of solids, with special consideration of finite specimen size in one dimension, is constructed. For materials in which nucleation occurs spatially randomly, phase change is predicted to decelerate when film thickness is reduced below the mean crystal grain size. This phenomenon originates from a reduction in the number of crystallites available to transform the surface as the sample becomes thinner. Good quantitative agreement between this simple model and the experimental data is attained using a minimum of kinetic parameters, suggesting it captures the essential physics of ASW

  12. Corrosion resistant amorphous metals and methods of forming corrosion resistant amorphous metals

    DOEpatents

    Farmer, Joseph C.; Wong, Frank M. G.; Haslam, Jeffery J.; Yang, Nancy; Lavernia, Enrique J.; Blue, Craig A.; Graeve, Olivia A.; Bayles, Robert; Perepezko, John H.; Kaufman, Larry; Schoenung, Julie; Ajdelsztajn, Leo

    2009-11-17

    A system for coating a surface comprises providing a source of amorphous metal, providing ceramic particles, and applying the amorphous metal and the ceramic particles to the surface by a spray. The coating comprises a composite material made of amorphous metal that contains one or more of the following elements in the specified range of composition: yttrium (.gtoreq.1 atomic %), chromium (14 to 18 atomic %), molybdenum (.gtoreq.7 atomic %), tungsten (.gtoreq.1 atomic %), boron (.ltoreq.5 atomic %), or carbon (.gtoreq.4 atomic %).

  13. Corrosion resistant amorphous metals and methods of forming corrosion resistant amorphous metals

    DOEpatents

    Farmer, Joseph C.; Wong, Frank M.G.; Haslam, Jeffery J.; Yang, Nancy; Lavernia, Enrique J.; Blue, Craig A.; Graeve, Olivia A.; Bayles, Robert; Perepezko, John H.; Kaufman, Larry; Schoenung, Julie; Ajdelsztajn, Leo

    2014-07-15

    A system for coating a surface comprises providing a source of amorphous metal, providing ceramic particles, and applying the amorphous metal and the ceramic particles to the surface by a spray. The coating comprises a composite material made of amorphous metal that contains one or more of the following elements in the specified range of composition: yttrium (.gtoreq.1 atomic %), chromium (14 to 18 atomic %), molybdenum (.gtoreq.7 atomic %), tungsten (.gtoreq.1 atomic %), boron (.ltoreq.5 atomic %), or carbon (.gtoreq.4 atomic %).

  14. Amorphization of silicon carbide by carbon displacement

    NASA Astrophysics Data System (ADS)

    Devanathan, R.; Gao, F.; Weber, W. J.

    2004-05-01

    We have used molecular dynamics simulations to examine the possibility of amorphizing silicon carbide (SiC) by exclusively displacing C atoms. At a defect generation corresponding to 0.2 displacements per atom, the enthalpy surpasses the level of melt-quenched SiC, the density decreases by about 15%, and the radial distribution function shows a lack of long-range order. Prior to amorphization, the surviving defects are mainly C Frenkel pairs (67%), but Si Frenkel pairs (18%) and antisite defects (15%) are also present. The results indicate that SiC can be amorphized by C sublattice displacements. Chemical short-range disorder, arising mainly from Frenkel pair production, plays a significant role in the amorphization.

  15. Amorphous Semiconductor Thin Films, an Introduction

    SciTech Connect

    Martin, Peter M.

    2003-12-01

    The field of amorphous semiconductors is so large that I cannot do it justice, but I hope this short column gives you some insight into the properties and materials available, and the issues involved.

  16. Fracture in Bulk Amorphous Alloys

    SciTech Connect

    Horton, J.A.; Wright, J.L.

    1998-11-30

    The fracture behavior of a Zr-based bulk amorphous alloy, Zr-10 AI-5 Ti-17.9 Cu-14.6 Ni, was examined by transmission electron microscopy (TEM) and x-ray diffraction for any evidence of crystallization preceding crack propagation. No evidence for crystallization was found in shear bands in compression specimens or at the fracture surface in tensile specimens. In- situ TEM deformation experiments were performed to more closely examine actual crack tip regions. During the in-situ deformation experiment controlled crack growth occurred to the point where the specimen was approximately 20 {micro}m thick at which point uncontrolled crack growth occurred. No evidence of any crystallization was found at the crack tips or the crack flanks. Subsequent scanning microscope examination showed that the uncontrolled crack growth region exhibited ridges and veins that appeared to have resulted from melting. Performing the deformations, both bulk and in-situ TEM, at liquid nitrogen temperatures (LN{sub 2}) resulted in an increase in the amount of controlled crack growth. The surface roughness of the bulk regions fractured at LN{sub 2} temperatures corresponded with the roughness of the crack propagation observed during the in-situ TEM experiment, suggesting that the smooth-appearing room temperature fracture sur-faces may also be a result of localized melting.

  17. Ductile crystalline–amorphous nanolaminates

    PubMed Central

    Wang, Yinmin; Li, Ju; Hamza, Alex V.; Barbee, Troy W.

    2007-01-01

    It is known that the room-temperature plastic deformation of bulk metallic glasses is compromised by strain softening and shear localization, resulting in near-zero tensile ductility. The incorporation of metallic glasses into engineering materials, therefore, is often accompanied by complete brittleness or an apparent loss of useful tensile ductility. Here we report the observation of an exceptional tensile ductility in crystalline copper/copper–zirconium glass nanolaminates. These nanocrystalline–amorphous nanolaminates exhibit a high flow stress of 1.09 ± 0.02 GPa, a nearly elastic-perfectly plastic behavior without necking, and a tensile elongation to failure of 13.8 ± 1.7%, which is six to eight times higher than that typically observed in conventional crystalline–crystalline nanolaminates (<2%) and most other nanocrystalline materials. Transmission electron microscopy and atomistic simulations demonstrate that shear banding instability no longer afflicts the 5- to 10-nm-thick nanolaminate glassy layers during tensile deformation, which also act as high-capacity sinks for dislocations, enabling absorption of free volume and free energy transported by the dislocations; the amorphous–crystal interfaces exhibit unique inelastic shear (slip) transfer characteristics, fundamentally different from those of grain boundaries. Nanoscale metallic glass layers therefore may offer great benefits in engineering the plasticity of crystalline materials and opening new avenues for improving their strength and ductility. PMID:17592136

  18. Ion-beam amorphization of semiconductors: A physical model based on the amorphous pocket population

    SciTech Connect

    Mok, K.R.C.; Jaraiz, M.; Martin-Bragado, I.; Rubio, J.E.; Castrillo, P.; Pinacho, R.; Barbolla, J.; Srinivasan, M.P.

    2005-08-15

    We introduce a model for damage accumulation up to amorphization, based on the ion-implant damage structures commonly known as amorphous pockets. The model is able to reproduce the silicon amorphous-crystalline transition temperature for C, Si, and Ge ion implants. Its use as an analysis tool reveals an unexpected bimodal distribution of the defect population around a characteristic size, which is larger for heavier ions. The defect population is split in both size and composition, with small, pure interstitial and vacancy clusters below the characteristic size, and amorphous pockets with a balanced mixture of interstitials and vacancies beyond that size.

  19. Amorphous Phases on the Surface of Mars

    NASA Technical Reports Server (NTRS)

    Rampe, E. B.; Morris, R. V.; Ruff, S. W.; Horgan, B.; Dehouck, E.; Achilles, C. N.; Ming, D. W.; Bish, D. L.; Chipera, S. J.

    2014-01-01

    Both primary (volcanic/impact glasses) and secondary (opal/silica, allophane, hisingerite, npOx, S-bearing) amorphous phases appear to be major components of martian surface materials based on orbital and in-situ measurements. A key observation is that whereas regional/global scale amorphous components include altered glass and npOx, local scale amorphous phases include hydrated silica/opal. This suggests widespread alteration at low water-to-rock ratios, perhaps due to snow/ice melt with variable pH, and localized alteration at high water-to-rock ratios. Orbital and in-situ measurements of the regional/global amorphous component on Mars suggests that it is made up of at least three phases: npOx, amorphous silicate (likely altered glass), and an amorphous S-bearing phase. Fundamental questions regarding the composition and the formation of the regional/global amorphous component(s) still remain: Do the phases form locally or have they been homogenized through aeolian activity and derived from the global dust? Is the parent glass volcanic, impact, or both? Are the phases separate or intimately mixed (e.g., as in palagonite)? When did the amorphous phases form? To address the question of source (local and/or global), we need to look for variations in the different phases within the amorphous component through continued modeling of the chemical composition of the amorphous phases in samples from Gale using CheMin and APXS data. If we find variations (e.g., a lack of or enrichment in amorphous silicate in some samples), this may imply a local source for some phases. Furthermore, the chemical composition of the weathering products may give insight into the formation mechanisms of the parent glass (e.g., impact glasses contain higher Al and lower Si [30], so we might expect allophane as a weathering product of impact glass). To address the question of whether these phases are separate or intimately mixed, we need to do laboratory studies of naturally altered samples made

  20. A Magnetic Sensor with Amorphous Wire

    PubMed Central

    He, Dongfeng; Shiwa, Mitsuharu

    2014-01-01

    Using a FeCoSiB amorphous wire and a coil wrapped around it, we have developed a sensitive magnetic sensor. When a 5 mm long amorphous wire with the diameter of 0.1 mm was used, the magnetic field noise spectrum of the sensor was about 30 pT/√Hz above 30 Hz. To show the sensitivity and the spatial resolution, the magnetic field of a thousand Japanese yen was scanned with the magnetic sensor. PMID:24940865

  1. Amorphous Carbon-Boron Nitride Nanotube Hybrids

    NASA Technical Reports Server (NTRS)

    Kim, Jae Woo (Inventor); Siochi, Emilie J. (Inventor); Wise, Kristopher E. (Inventor); Lin, Yi (Inventor); Connell, John (Inventor)

    2016-01-01

    A method for joining or repairing boron nitride nanotubes (BNNTs). In joining BNNTs, the nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation to form well bonded hybrid a-C/BNNT structures. In repairing BNNTs, the damaged site of the nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation to form well bonded hybrid a-C/BNNT structures at the damage site.

  2. Thermal transport in amorphous materials: a review

    NASA Astrophysics Data System (ADS)

    Wingert, Matthew C.; Zheng, Jianlin; Kwon, Soonshin; Chen, Renkun

    2016-11-01

    Thermal transport plays a crucial role in performance and reliability of semiconductor electronic devices, where heat is mainly carried by phonons. Phonon transport in crystalline semiconductor materials, such as Si, Ge, GaAs, GaN, etc, has been extensively studied over the past two decades. In fact, study of phonon physics in crystalline semiconductor materials in both bulk and nanostructure forms has been the cornerstone of the emerging field of ‘nanoscale heat transfer’. On the contrary, thermal properties of amorphous materials have been relatively less explored. Recently, however, a growing number of studies have re-examined the thermal properties of amorphous semiconductors, such as amorphous Si. These studies, which included both computational and experimental work, have revealed that phonon transport in amorphous materials is perhaps more complicated than previously thought. For instance, depending on the type of amorphous materials, thermal transport occurs via three types of vibrations: propagons, diffusons, and locons, corresponding to the propagating, diffusion, and localized modes, respectively. The relative contribution of each of these modes dictates the thermal conductivity of the material, including its magnitude and its dependence on sample size and temperature. In this article, we will review the fundamental principles and recent development regarding thermal transport in amorphous semiconductors.

  3. Amorphous boron nitride at high pressure

    NASA Astrophysics Data System (ADS)

    Durandurdu, Murat

    2016-06-01

    The pressure-induced phase transformation in hexagonal boron nitrite and amorphous boron nitrite is studied using ab initio molecular dynamics simulations. The hexagonal-to-wurtzite phase transformation is successfully reproduced in the simulation with a transformation mechanism similar to one suggested in experiment. Amorphous boron nitrite, on the other hand, gradually transforms to a high-density amorphous phase with the application of pressure. This phase transformation is irreversible because a densified amorphous state having both sp3 and sp2 bonds is recovered upon pressure release. The high-density amorphous state mainly consists of sp3 bonds and its local structure is quite similar to recently proposed intermediate boron nitrite phases, in particular tetragonal structure (P42/mnm), rather than the known the wurtzite or cubic boron nitrite due to the existence of four membered rings and edge sharing connectivity. On the basis of this finding we propose that amorphous boron nitrite might be best candidate as a starting structure to synthesize the intermediate phase(s) at high pressure and temperature (probably below 800 °C) conditions.

  4. Wear Resistant Amorphous and Nanocomposite Steel Coatings

    SciTech Connect

    Branagan, Daniel James; Swank, William David; Haggard, Delon C; Fincke, James Russell; Sordelet, D.

    2001-10-01

    In this article, amorphous and nanocomposite thermally deposited steel coatings have been formed by using both plasma and high-velocity oxy-fuel (HVOF) spraying techniques. This was accomplished by developing a specialized iron-based composition with a low critical cooling rate (?104 K/s) for metallic glass formation, processing the alloy by inert gas atomization to form micron-sized amorphous spherical powders, and then spraying the classified powder to form coatings. A primarily amorphous structure was formed in the as-sprayed coatings, independent of coating thickness. After a heat treatment above the crystallization temperature (568°C), the structure of the coatings self-assembled (i.e., devitrified) into a multiphase nanocomposite microstructure with 75 to 125 nm grains containing a distribution of 20 nm second-phase grain-boundary precipitates. Vickers microhardness testing revealed that the amorphous coatings were very hard (10.2 to 10.7 GPa), with further increases in hardness after devitrification (11.4 to 12.8 GPa). The wear characteristics of the amorphous and nanocomposite coatings were determined using both two-body pin-on-disk and three-body rubber wheel wet-slurry sand tests. The results indicate that the amorphous and nanocomposite steel coatings are candidates for a wide variety of wear-resistant applications.

  5. Electrons and phonons in amorphous semiconductors

    NASA Astrophysics Data System (ADS)

    Prasai, Kiran; Biswas, Parthapratim; Drabold, D. A.

    2016-07-01

    The coupling between lattice vibrations and electrons is one of the central concepts of condensed matter physics. The subject has been deeply studied for crystalline materials, but far less so for amorphous and glassy materials, which are among the most important for applications. In this paper, we explore the electron-lattice coupling using current tools of a first-principles computer simulation. We choose three materials to illustrate the phenomena: amorphous silicon (a-Si), amorphous selenium (a-Se) and amorphous gallium nitride (a-GaN). In each case, we show that there is a strong correlation between the localization of electron states and the magnitude of thermally induced fluctuations in energy eigenvalues obtained from the density-functional theory (i.e. Kohn–Sham eigenvalues). We provide a heuristic theory to explain these observations. The case of a-GaN, a topologically disordered partly ionic insulator, is distinctive compared to the covalent amorphous examples. Next, we explore the consequences of changing the charge state of a system as a proxy for tracking photo-induced structural changes in the materials. Where transport is concerned, we lend insight into the Meyer–Neldel compensation rule and discuss a thermally averaged Kubo–Greenwood formula as a means to estimate electrical conductivity and especially its temperature dependence. We close by showing how the optical gap of an amorphous semiconductor can be computationally engineered with the judicious use of Hellmann–Feynman forces (associated with a few defect states) using molecular dynamics simulations. These forces can be used to close or open an optical gap, and identify a structure with a prescribed gap. We use the approach with plane-wave density functional methods to identify a low-energy amorphous phase of silicon including several coordination defects, yet with a gap close to that of good quality a-Si models.

  6. Electrons and phonons in amorphous semiconductors

    NASA Astrophysics Data System (ADS)

    Prasai, Kiran; Biswas, Parthapratim; Drabold, D. A.

    2016-07-01

    The coupling between lattice vibrations and electrons is one of the central concepts of condensed matter physics. The subject has been deeply studied for crystalline materials, but far less so for amorphous and glassy materials, which are among the most important for applications. In this paper, we explore the electron-lattice coupling using current tools of a first-principles computer simulation. We choose three materials to illustrate the phenomena: amorphous silicon (a-Si), amorphous selenium (a-Se) and amorphous gallium nitride (a-GaN). In each case, we show that there is a strong correlation between the localization of electron states and the magnitude of thermally induced fluctuations in energy eigenvalues obtained from the density-functional theory (i.e. Kohn-Sham eigenvalues). We provide a heuristic theory to explain these observations. The case of a-GaN, a topologically disordered partly ionic insulator, is distinctive compared to the covalent amorphous examples. Next, we explore the consequences of changing the charge state of a system as a proxy for tracking photo-induced structural changes in the materials. Where transport is concerned, we lend insight into the Meyer-Neldel compensation rule and discuss a thermally averaged Kubo-Greenwood formula as a means to estimate electrical conductivity and especially its temperature dependence. We close by showing how the optical gap of an amorphous semiconductor can be computationally engineered with the judicious use of Hellmann-Feynman forces (associated with a few defect states) using molecular dynamics simulations. These forces can be used to close or open an optical gap, and identify a structure with a prescribed gap. We use the approach with plane-wave density functional methods to identify a low-energy amorphous phase of silicon including several coordination defects, yet with a gap close to that of good quality a-Si models.

  7. Iron-based amorphous alloys and methods of synthesizing iron-based amorphous alloys

    DOEpatents

    Saw, Cheng Kiong; Bauer, William A.; Choi, Jor-Shan; Day, Dan; Farmer, Joseph C.

    2016-05-03

    A method according to one embodiment includes combining an amorphous iron-based alloy and at least one metal selected from a group consisting of molybdenum, chromium, tungsten, boron, gadolinium, nickel phosphorous, yttrium, and alloys thereof to form a mixture, wherein the at least one metal is present in the mixture from about 5 atomic percent (at %) to about 55 at %; and ball milling the mixture at least until an amorphous alloy of the iron-based alloy and the at least one metal is formed. Several amorphous iron-based metal alloys are also presented, including corrosion-resistant amorphous iron-based metal alloys and radiation-shielding amorphous iron-based metal alloys.

  8. Amorphous Diamond MEMS and Sensors

    SciTech Connect

    SULLIVAN, JOHN P.; FRIEDMANN, THOMAS A.; ASHBY, CAROL I.; DE BOER, MAARTEN P.; SCHUBERT, W. KENT; SHUL, RANDY J.; HOHLFELDER, ROBERT J.; LAVAN, D.A.

    2002-06-01

    This report describes a new microsystems technology for the creation of microsensors and microelectromechanical systems (MEMS) using stress-free amorphous diamond (aD) films. Stress-free aD is a new material that has mechanical properties close to that of crystalline diamond, and the material is particularly promising for the development of high sensitivity microsensors and rugged and reliable MEMS. Some of the unique properties of aD include the ability to easily tailor film stress from compressive to slightly tensile, hardness and stiffness 80-90% that of crystalline diamond, very high wear resistance, a hydrophobic surface, extreme chemical inertness, chemical compatibility with silicon, controllable electrical conductivity from insulating to conducting, and biocompatibility. A variety of MEMS structures were fabricated from this material and evaluated. These structures included electrostatically-actuated comb drives, micro-tensile test structures, singly- and doubly-clamped beams, and friction and wear test structures. It was found that surface micromachined MEMS could be fabricated in this material easily and that the hydrophobic surface of the film enabled the release of structures without the need for special drying procedures or the use of applied hydrophobic coatings. Measurements using these structures revealed that aD has a Young's modulus of {approx}650 GPa, a tensile fracture strength of 8 GPa, and a fracture toughness of 8 MPa{center_dot}m {sup 1/2}. These results suggest that this material may be suitable in applications where stiction or wear is an issue. Flexural plate wave (FPW) microsensors were also fabricated from aD. These devices use membranes of aD as thin as {approx}100 nm. The performance of the aD FPW sensors was evaluated for the detection of volatile organic compounds using ethyl cellulose as the sensor coating. For comparable membrane thicknesses, the aD sensors showed better performance than silicon nitride based sensors. Greater than

  9. Amorphous Silicon Based Neutron Detector

    SciTech Connect

    Xu, Liwei

    2004-12-12

    Various large-scale neutron sources already build or to be constructed, are important for materials research and life science research. For all these neutron sources, neutron detectors are very important aspect. However, there is a lack of a high-performance and low-cost neutron beam monitor that provides time and temporal resolution. The objective of this SBIR Phase I research, collaboratively performed by Midwest Optoelectronics, LLC (MWOE), the University of Toledo (UT) and Oak Ridge National Laboratory (ORNL), is to demonstrate the feasibility for amorphous silicon based neutron beam monitors that are pixilated, reliable, durable, fully packaged, and fabricated with high yield using low-cost method. During the Phase I effort, work as been focused in the following areas: 1) Deposition of high quality, low-defect-density, low-stress a-Si films using very high frequency plasma enhanced chemical vapor deposition (VHF PECVD) at high deposition rate and with low device shunting; 2) Fabrication of Si/SiO2/metal/p/i/n/metal/n/i/p/metal/SiO2/ device for the detection of alpha particles which are daughter particles of neutrons through appropriate nuclear reactions; and 3) Testing of various devices fabricated for alpha and neutron detection; As the main results: · High quality, low-defect-density, low-stress a-Si films have been successfully deposited using VHF PECVD on various low-cost substrates; · Various single-junction and double junction detector devices have been fabricated; · The detector devices fabricated have been systematically tested and analyzed. · Some of the fabricated devices are found to successfully detect alpha particles. Further research is required to bring this Phase I work beyond the feasibility demonstration toward the final prototype devices. The success of this project will lead to a high-performance, low-cost, X-Y pixilated neutron beam monitor that could be used in all of the neutron facilities worldwide. In addition, the technologies

  10. Understanding Thermal Conductivity in Amorphous Materials

    NASA Astrophysics Data System (ADS)

    Kommandur, Sampath; Yee, Shannon

    2014-03-01

    Current energy technologies such as thermoelectrics, photovoltaics, and LEDs make extensive use of amorphous materials and are limited by heat transfer. Device improvements necessitate a better understanding of the thermal conductivity in amorphous materials. While there are basic theories that capture the trends in thermal conductivity of a select set of amorphous materials, a general framework is needed to explain the fundamental transport of heat in all amorphous materials. One empirical theory that has been successful at describing the thermal conductivity in some materials is the k-min model, however, assumptions in that model limit its generalizability. Another theory defines the existence of propagons, diffusons, and locons, which constitute vibrational modes that carry heat. Our work first presents a summary of literature on the thermal conductivity in amorphous materials and then compares those theories to a breadth of experimental data. Based upon those results, a generic model is proposed that is widely applicable with the ultimate goal of this work being to describe the temperature dependent thermal conductivity of polymers. -/abstract- Sampath Kommandur and Shannon K. Yee 21.1.1: Thermoelectric Phenomena, Materials, Devices, and Applications (GER

  11. SURVIVAL OF AMORPHOUS WATER ICE ON CENTAURS

    SciTech Connect

    Guilbert-Lepoutre, Aurelie

    2012-10-01

    Centaurs are believed to be Kuiper Belt objects in transition between Jupiter and Neptune before possibly becoming Jupiter family comets. Some indirect observational evidence is consistent with the presence of amorphous water ice in Centaurs. Some of them also display a cometary activity, probably triggered by the crystallization of the amorphous water ice, as suggested by Jewitt and this work. Indeed, we investigate the survival of amorphous water ice against crystallization, using a fully three-dimensional thermal evolution model. Simulations are performed for varying heliocentric distances and obliquities. They suggest that crystallization can be triggered as far as 16 AU, though amorphous ice can survive beyond 10 AU. The phase transition is an efficient source of outgassing up to 10-12 AU, which is broadly consistent with the observations of the active Centaurs. The most extreme case is 167P/CINEOS, which barely crystallizes in our simulations. However, amorphous ice can be preserved inside Centaurs in many heliocentric distance-obliquity combinations, below a {approx}5-10 m crystallized crust. We also find that outgassing due to crystallization cannot be sustained for a time longer than 10{sup 4}-10{sup 4} years, leading to the hypothesis that active Centaurs might have recently suffered from orbital changes. This could be supported by both observations (although limited) and dynamical studies.

  12. Synthesis method for amorphous metallic foam

    NASA Astrophysics Data System (ADS)

    Schroers, Jan; Veazey, Chris; Demetriou, Marios D.; Johnson, William L.

    2004-12-01

    A synthesis method for the production of amorphous metallic foam is introduced. This method utilizes the thermodynamic stability and thermoplastic formability of the supercooled liquid state to produce low-density amorphous metallic foams in dimensions that are not limited to the critical casting thickness. The method consists of three stages: the prefoaming stage, in which a large number of small bubbles are created in the equilibrium liquid under pressure; the quenching stage, in which the liquid prefoam is quenched to its amorphous state; the foam expansion stage, in which the amorphous prefoam is reheated to the supercooled liquid region and is processed under pressures substantially lower than those applied in the prefoaming step. Results from a dynamic model suggest that the foam expansion process is feasible, as the kinetics of bubble expansion in the supercooled liquid region are faster than the kinetics of crystallization. Within the proposed synthesis method, bulk amorphous foam products characterized by bubble volume fractions of as high as 85% are successfully produced.

  13. Amorphous metallic films in silicon metallization systems

    NASA Technical Reports Server (NTRS)

    So, F.; Kolawa, E.; Nicolet, M. A.

    1985-01-01

    Diffusion barrier research was focussed on lowering the chemical reactivity of amorphous thin films on silicon. An additional area of concern is the reaction with metal overlays such as aluminum, silver, and gold. Gold was included to allow for technology transfer to gallium arsenide PV cells. Amorphous tungsten nitride films have shown much promise. Stability to annealing temperatures of 700, 800, and 550 C were achieved for overlays of silver, gold, and aluminum, respectively. The lower results for aluminum were not surprising because there is an eutectic that can form at a lower temperature. It seems that titanium and zirconium will remove the nitrogen from a tungsten nitride amorphous film and render it unstable. Other variables of research interest were substrate bias and base pressure during sputtering.

  14. Phase transitions in biogenic amorphous calcium carbonate.

    PubMed

    Gong, Yutao U T; Killian, Christopher E; Olson, Ian C; Appathurai, Narayana P; Amasino, Audra L; Martin, Michael C; Holt, Liam J; Wilt, Fred H; Gilbert, P U P A

    2012-04-17

    Crystalline biominerals do not resemble faceted crystals. Current explanations for this property involve formation via amorphous phases. Using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy (PEEM), here we examine forming spicules in embryos of Strongylocentrotus purpuratus sea urchins, and observe a sequence of three mineral phases: hydrated amorphous calcium carbonate (ACC · H(2)O) → dehydrated amorphous calcium carbonate (ACC) → calcite. Unexpectedly, we find ACC · H(2)O-rich nanoparticles that persist after the surrounding mineral has dehydrated and crystallized. Protein matrix components occluded within the mineral must inhibit ACC · H(2)O dehydration. We devised an in vitro, also using XANES-PEEM, assay to identify spicule proteins that may play a role in stabilizing various mineral phases, and found that the most abundant occluded matrix protein in the sea urchin spicules, SM50, stabilizes ACC · H(2)O in vitro. PMID:22492931

  15. IUE observations of amorphous hot galaxies

    NASA Technical Reports Server (NTRS)

    Lamb, S. A.; Hjellming, M. S.; Gallagher, J. S., III; Hunter, D. A.

    1985-01-01

    Blue amorphous galaxies are star-forming, irregularlike systems which lack the spatially distinct OB stellar groups that are characteristic of most late-type galaxies. In order to better understand the nature of star-formation processes in these unusual galaxies, short-wavelength IUE spectra of the amorphous galaxies NGC 1705 and NGC 1800 have been obtained. It is found that NGC 1705 contains a normal mix of OB stars, which is consistent with the nearly constant recent star-formation rate inferred from new optical data. NGC 1800 is likely to have similar properties, and blue galaxies with amorphous structures thus do not show evidence for anomalies in stellar populations. The UV spectra of these galaxies and a variety of other hot extragalactic stellar systems in fact have similar characteristics, which suggests OB stellar populations are often homogeneous in their properties.

  16. Synthesis and photocurrent of amorphous boron nanowires.

    PubMed

    Ge, Liehui; Lei, Sidong; Hart, Amelia H C; Gao, Guanhui; Jafry, Huma; Vajtai, Robert; Ajayan, Pulickel M

    2014-08-22

    Although theoretically feasible, synthesis of boron nanostructures is challenging due to the highly reactive nature, high melting and boiling points of boron. We have developed a thermal vapor transfer approach to synthesizing amorphous boron nanowire using a solid boron source. The amorphous nature and chemical composition of boron nanowires were characterized by high resolution transmission electron microscopy, selected area electron diffraction, and electron energy loss spectroscopy. Optical properties and photoconduction of boron nanowires have not yet been reported. In our investigation, the amorphous boron nanowire showed much better optical and electrical properties than previously reported photo-response of crystalline boron nanobelts. When excited by a blue LED, the photo/dark current ratio (I/I₀) is 1.5 and time constants in the order of tens of seconds. I/I₀ is 1.17 using a green light. PMID:25061013

  17. Superior radiation tolerant materials: Amorphous silicon oxycarbide

    NASA Astrophysics Data System (ADS)

    Nastasi, Michael; Su, Qing; Price, Lloyd; Colón Santana, Juan A.; Chen, Tianyi; Balerio, Robert; Shao, Lin

    2015-06-01

    We studied the radiation tolerance of amorphous silicon oxycarbide (SiOC) alloys by combining ion irradiation, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The amorphous SiOC alloys thin films were grown via co-sputtering from SiO2 and SiC (amorphous phase) targets either on a surface oxidized Si (100) substrate or on a sodium chloride substrate. By controlling the sputtering rate of each target, SiOC alloys with different compositions (1:2, 1:1, 2:1 ratios) were obtained. These alloys were irradiated by 100 keV He+ ions at both room temperature and 600 °C with damage levels ranging from 1 to 20 displacements per atom (dpa). TEM characterization shows no sign of crystallization, void formation or segregation in all irradiated samples. Our findings suggest that SiOC alloys are a class of promising radiation-tolerant materials.

  18. Enthalpy of crystallization of amorphous yttrium oxide

    SciTech Connect

    Reznitskii, L.A.

    1988-02-01

    Measurements have been made on the enthalpies of crystallization of amorphous Fe/sub 2/O/sub 3/ and Y/sub 3/Fe/sub 5/O/sub 12/ from amorphous Fe/sub 2/O/sub 3/ and Y/sub 2/O/sub 3/ as determined by the DSC method. The heat of crystallization for Y/sub 2/O/sub 3am/ does not make itself felt on the heating thermogram, in contrast to that for Fe/sub 2/O/sub 3/, evidently because it is spread out over a wide temperature range, so it is difficult to measure. One can combine thermochemical equations to calculate the enthalpy of crystallization for amorphous yttrium oxide as ..delta..H = -24.9 kJ/mole.

  19. The Phagocytosis and Toxicity of Amorphous Silica

    PubMed Central

    Costantini, Lindsey M.; Gilberti, Renée M.; Knecht, David A.

    2011-01-01

    Background Inhalation of crystalline silica is known to cause an inflammatory reaction and chronic exposure leads to lung fibrosis and can progress into the disease, silicosis. Cultured macrophages bind crystalline silica particles, phagocytose them, and rapidly undergo apoptotic and necrotic death. The mechanism by which particles are bound and internalized and the reason particles are toxic is unclear. Amorphous silica has been considered to be a less toxic form, but this view is controversial. We compared the uptake and toxicity of amorphous silica to crystalline silica. Methodology/Principal Findings Amorphous silica particles are phagocytosed by macrophage cells and a single internalized particle is capable of killing a cell. Fluorescent dextran is released from endo-lysosomes within two hours after silica treatment and Caspase-3 activation occurs within 4 hours. Interestingly, toxicity is specific to macrophage cell lines. Other cell types are resistant to silica particle toxicity even though they internalize the particles. The large and uniform size of the spherical, amorphous silica particles allowed us to monitor them during the uptake process. In mCherry-actin transfected macrophages, actin rings began to form 1-3 minutes after silica binding and the actin coat disassembled rapidly following particle internalization. Pre-loading cells with fluorescent dextran allowed us to visualize the fusion of phagosomes with endosomes during internalization. These markers provided two new ways to visualize and quantify particle internalization. At 37°C the rate of amorphous silica internalization was very rapid regardless of particle coating. However, at room temperature, opsonized silica is internalized much faster than non-opsonized silica. Conclusions/Significance Our results indicate that amorphous and crystalline silica are both phagocytosed and both toxic to mouse alveolar macrophage (MH-S) cells. The pathway leading to apoptosis appears to be similar in both

  20. Cooling of hot electrons in amorphous silicon

    SciTech Connect

    Vanderhaghen, R.; Hulin, D.; Cuzeau, S.; White, J.O.

    1997-07-01

    Measurements of the cooling rate of hot carriers in amorphous silicon are made with a two-pump, one-probe technique. The experiment is simulated with a rate-equation model describing the energy transfer between a population of hot carriers and the lattice. An energy transfer rate proportional to the temperature difference is found to be consistent with the experimental data while an energy transfer independent of the temperature difference is not. This contrasts with the situation in crystalline silicon. The measured cooling rates are sufficient to explain the difficulty in observing avalanche effects in amorphous silicon.

  1. Thermal conductivity of sputtered amorphous Ge films

    SciTech Connect

    Zhan, Tianzhuo; Xu, Yibin; Goto, Masahiro; Tanaka, Yoshihisa; Kato, Ryozo; Sasaki, Michiko; Kagawa, Yutaka

    2014-02-15

    We measured the thermal conductivity of amorphous Ge films prepared by magnetron sputtering. The thermal conductivity was significantly higher than the value predicted by the minimum thermal conductivity model and increased with deposition temperature. We found that variations in sound velocity and Ge film density were not the main factors in the high thermal conductivity. Fast Fourier transform patterns of transmission electron micrographs revealed that short-range order in the Ge films was responsible for their high thermal conductivity. The results provide experimental evidences to understand the underlying nature of the variation of phonon mean free path in amorphous solids.

  2. Production feature of soft magnetic amorphous alloys

    NASA Astrophysics Data System (ADS)

    Tyagunov, A. G.; Baryshev, E. E.; Shmakova, K. Yu

    2016-06-01

    Methods for making nanocrystalline alloys have been discussed. Temperature dependences of the surface tension (σ), electric resistivity (ρ), magnetic susceptibility (χ) and kinematic viscosity (ν) have been obtained. Comparison of the properties of amorphous ribbons obtained by the pilot and serial technologies has been conducted. Science-based technology of multi-component alloy smelting makes it possible to prepare equilibrium smelt, the structure of which has a significant effect on the properties of the amorphous ribbon before spinning and kinetics of its crystallization has been offered.

  3. Ion bombardment and disorder in amorphous silicon

    SciTech Connect

    Sidhu, L.S.; Gaspari, F.; Zukotynski, S.

    1997-07-01

    The effect of ion bombardment during growth on the structural and optical properties of amorphous silicon are presented. Two series of films were deposited under electrically grounded and positively biased substrate conditions. The biased samples displayed lower growth rates and increased hydrogen content relative to grounded counterparts. The film structure was examined using Raman spectroscopy. The transverse optic like phonon band position was used as a parameter to characterize network order. Biased samples displayed an increased order of the amorphous network relative to grounded samples. Furthermore, biased samples exhibited a larger optical gap. These results are correlated and attributed to reduced ion bombardment effects.

  4. Short range order in amorphous polycondensates

    SciTech Connect

    Lamers, C.; Richter, D.; Schweika, W.; Batoulis, J.; Sommer, K.; Cable, J.W.; Shapiro, S.M.

    1992-12-01

    The static coherent structure factors S(Q) of the polymer glass Bisphenol-A-Polycarbonate and its chemical variation Bisphenol-A- Polyctherkctone- both in differently deuterated versions- have been measured by spin polarized neutron scattering. The method of spin polarization analysis provided an experimental separation of coherent and incoherent scattering and a reliable intensity calibration. Results are compared to structure factors calculated for model structures which were obtained by ``amorphous cell`` computer simulations. In general reasonable agreement is found between experiment and simulation; however, certain discrepancies hint at an insufficient structural relaxation in the amorphous cell method. 15 refs, 1 fig, 1 tab.

  5. Amorphous Insulator Films With Controllable Properties

    NASA Technical Reports Server (NTRS)

    Alterovitz, Samuel A.; Warner, Joseph D.; Liu, David C.; Pouch, John J.

    1987-01-01

    In experiments described in report, amorphous hydrogenated carbon films grown at room temperature by low-frequency plasma deposition, using methane or butane gas. Films have unique array of useful properties; (a) adhere to wide variety of materials; (b) contain only carbon and hydrogen; (c) smooth and free of pinholes; (d) resistant to attack by moisture and chemicals; and (e) have high electric-breakdown strength and electrical resistivity. Two of optical properties and hardness of this film controlled by deposition conditions. Amorphous a-C:H and BN films used for hermetic sealing and protection of optical, electronic, magnetic, or delicate mechanical systems, and for semiconductor field dielectrics.

  6. New Amorphous Silicon Alloy Systems

    NASA Astrophysics Data System (ADS)

    Kapur, Mridula N.

    1990-01-01

    The properties of hydrogenated amorphous silicon (a-Si:H) have been modified by alloying with Al, Ga and S respectively. The Al and Ga alloys are in effect quaternary alloys as they were fabricated in a carbon-rich discharge. The alloys were prepared by the plasma assisted chemical vapor deposition (PACVD) method. This method has several advantages, the major one being the relatively low defect densities of the resulting materials. The PACVD system used to grow the alloy films was designed and constructed in the laboratory. It was first tested with known (a-Si:H and a-Si:As:H) materials. Thus, it was established that device quality alloy films could be grown with the home-made PACVD setup. The chemical composition of the alloys was characterized by secondary ion mass spectrometry (SIMS), and electron probe microanalysis (EPMA). The homogeneous nature of hydrogen distribution in the alloys was established by SIMS depth profile analysis. A quantitative analysis of the bulk elemental content was carried out by EPMA. The analysis indicated that the alloying element was incorporated in the films more efficiently at low input gas concentrations than at the higher concentrations. A topological model was proposed to explain the observed behavior. The optical energy gap of the alloys could be varied in the 0.90 to 1.92 eV range. The Al and Ga alloys were low band gap materials, whereas alloying with S had the effect of widening the energy gap. It was observed that although the Si-Al and Si-Ga alloys contained significant amounts of C and H, the magnitude of the energy gap was determined by the metallic component. The various trends in optical properties could be related to the binding characteristics of the respective alloy systems. A quantitative explanation of the results was provided by White's tight binding model. The dark conductivity-temperature dependence of the alloys was examined. A linear dependence was observed for the Al and Ga systems. Electronic conduction in

  7. Amorphization and nanocrystallization of silcon under shock compression

    SciTech Connect

    Remington, B. A.; Wehrenberg, C. E.; Zhao, S.; Hahn, E. N.; Kad, B.; Bringa, E. M.; Meyers, M. A.

    2015-11-06

    High-power, short-duration, laser-driven, shock compression and recovery experiments on [001] silicon unveiled remarkable structural changes above a pressure threshold. Two distinct amorphous regions were identified: (a) a bulk amorphous layer close to the surface and (b) amorphous bands initially aligned with {111} slip planes. Further increase of the laser energy leads to the re-crystallization of amorphous silicon into nanocrystals with high concentration of nano-twins. This amorphization is produced by the combined effect of high magnitude hydrostatic and shear stresses under dynamic shock compression. Shock-induced defects play a very important role in the onset of amorphization. Calculations of the free energy changes with pressure and shear, using the Patel-Cohen methodology, are in agreement with the experimental results. Molecular dynamics simulation corroborates the amorphization, showing that it is initiated by the nucleation and propagation of partial dislocations. As a result, the nucleation of amorphization is analyzed qualitatively by classical nucleation theory.

  8. Inverted amorphous silicon solar cell utilizing cermet layers

    DOEpatents

    Hanak, Joseph J.

    1979-01-01

    An amorphous silicon solar cell incorporating a transparent high work function metal cermet incident to solar radiation and a thick film cermet contacting the amorphous silicon opposite to said incident surface.

  9. 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.

  10. 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.

  11. Excess specific heat in evaporated amorphous silicon.

    PubMed

    Queen, D R; Liu, X; Karel, J; Metcalf, T H; Hellman, F

    2013-03-29

    The specific heat C of e-beam evaporated amorphous silicon (a-Si) thin films prepared at various growth temperatures T(S) and thicknesses t was measured from 2 to 300 K, along with sound velocity v, shear modulus G, density n(Si), and Raman spectra. Increasing T(S) results in a more ordered amorphous network with increases in n(Si), v, G, and a decrease in bond angle disorder. Below 20 K, an excess C is seen in films with less than full density where it is typical of an amorphous solid, with both a linear term characteristic of two-level systems (TLS) and an additional (non-Debye) T3 contribution. The excess C is found to be independent of the elastic properties but to depend strongly on density. The density dependence suggests that low energy glassy excitations can form in a-Si but only in microvoids or low density regions and are not intrinsic to the amorphous silicon network. A correlation is found between the density of TLS n0 and the excess T3 specific heat c(ex) suggesting that they have a common origin.

  12. Metal electrode for amorphous silicon solar cells

    DOEpatents

    Williams, Richard

    1983-01-01

    An amorphous silicon solar cell having an N-type region wherein the contact to the N-type region is composed of a material having a work function of about 3.7 electron volts or less. Suitable materials include strontium, barium and magnesium and rare earth metals such as gadolinium and yttrium.

  13. Transient amorphous calcium phosphate in forming enamel.

    PubMed

    Beniash, Elia; Metzler, Rebecca A; Lam, Raymond S K; Gilbert, P U P A

    2009-05-01

    Enamel, the hardest tissue in the body, begins as a three-dimensional network of nanometer size mineral particles, suspended in a protein gel. This mineral network serves as a template for mature enamel formation. To further understand the mechanisms of enamel formation we characterized the forming enamel mineral at an early secretory stage using X-ray absorption near-edge structure (XANES) spectromicroscopy, transmission electron microscopy (TEM), FTIR microspectroscopy and polarized light microscopy. We show that the newly formed enamel mineral is amorphous calcium phosphate (ACP), which eventually transforms into apatitic crystals. Interestingly, the size, shape and spatial organization of these amorphous mineral particles and older crystals are essentially the same, indicating that the mineral morphology and organization in enamel is determined prior to its crystallization. Mineralization via transient amorphous phases has been previously reported in chiton teeth, mollusk shells, echinoderm spicules and spines, and recent reports strongly suggest the presence of transient amorphous mineral in forming vertebrate bones. The present finding of transient ACP in murine tooth enamel suggests that this strategy might be universal. PMID:19217943

  14. Plasma deposition of amorphous metal alloys

    DOEpatents

    Hays, A.K.

    1979-07-18

    Amorphous metal alloy coatings are plasma-deposited by dissociation of vapors of organometallic compounds and metalloid hydrides in the presence of a reducing gas, using a glow discharge. Tetracarbonylnickel, phosphine, and hydrogen constitute a typical reaction mixture of the invention, yielding a NiPC alloy.

  15. Amorphous silica-like carbon dioxide.

    PubMed

    Santoro, Mario; Gorelli, Federico A; Bini, Roberto; Ruocco, Giancarlo; Scandolo, Sandro; Crichton, Wilson A

    2006-06-15

    Among the group IV elements, only carbon forms stable double bonds with oxygen at ambient conditions. At variance with silica and germania, the non-molecular single-bonded crystalline form of carbon dioxide, phase V, only exists at high pressure. The amorphous forms of silica (a-SiO2) and germania (a-GeO2) are well known at ambient conditions; however, the amorphous, non-molecular form of CO2 has so far been described only as a result of first-principles simulations. Here we report the synthesis of an amorphous, silica-like form of carbon dioxide, a-CO2, which we call 'a-carbonia'. The compression of the molecular phase III of CO2 between 40 and 48 GPa at room temperature initiated the transformation to the non-molecular amorphous phase. Infrared spectra measured at temperatures up to 680 K show the progressive formation of C-O single bonds and the simultaneous disappearance of all molecular signatures. Furthermore, state-of-the-art Raman and synchrotron X-ray diffraction measurements on temperature-quenched samples confirm the amorphous character of the material. Comparison with vibrational and diffraction data for a-SiO2 and a-GeO2, as well as with the structure factor calculated for the a-CO2 sample obtained by first-principles molecular dynamics, shows that a-CO2 is structurally homologous to the other group IV dioxide glasses. We therefore conclude that the class of archetypal network-forming disordered systems, including a-SiO2, a-GeO2 and water, must be extended to include a-CO2. PMID:16778885

  16. Pressure-induced amorphous-to-amorphous configuration change in Ca-Al metallic glasses

    PubMed Central

    Lou, H. B.; Fang, Y. K.; Zeng, Q. S.; Lu, Y. H.; Wang, X. D.; Cao, Q. P.; Yang, K.; Yu, X. H.; Zheng, L.; Zhao, Y. D.; Chu, W. S.; Hu, T. D.; Wu, Z. Y.; Ahuja, R.; Jiang, J. Z.

    2012-01-01

    Pressure-induced amorphous-to-amorphous configuration changes in Ca-Al metallic glasses (MGs) were studied by performing in-situ room-temperature high-pressure x-ray diffraction up to about 40 GPa. Changes in compressibility at about 18 GPa, 15.5 GPa and 7.5 GPa during compression are detected in Ca80Al20, Ca72.7Al27.3, and Ca66.4Al33.6 MGs, respectively, whereas no clear change has been detected in the Ca50Al50 MG. The transfer of s electrons into d orbitals under pressure, reported for the pressure-induced phase transformations in pure polycrystalline Ca, is suggested to explain the observation of an amorphous-to-amorphous configuration change in this Ca-Al MG system. Results presented here show that the pressure induced amorphous-to-amorphous configuration is not limited to f electron-containing MGs. PMID:22530094

  17. Fabricating amorphous silicon solar cells by varying the temperature _of the substrate during deposition of the amorphous silicon layer

    DOEpatents

    Carlson, David E.

    1982-01-01

    An improved process for fabricating amorphous silicon solar cells in which the temperature of the substrate is varied during the deposition of the amorphous silicon layer is described. Solar cells manufactured in accordance with this process are shown to have increased efficiencies and fill factors when compared to solar cells manufactured with a constant substrate temperature during deposition of the amorphous silicon layer.

  18. Defect-induced solid state amorphization of molecular crystals

    NASA Astrophysics Data System (ADS)

    Lei, Lei; Carvajal, Teresa; Koslowski, Marisol

    2012-04-01

    We investigate the process of mechanically induced amorphization in small molecule organic crystals under extensive deformation. In this work, we develop a model that describes the amorphization of molecular crystals, in which the plastic response is calculated with a phase field dislocation dynamics theory in four materials: acetaminophen, sucrose, γ-indomethacin, and aspirin. The model is able to predict the fraction of amorphous material generated in single crystals for a given applied stress. Our results show that γ-indomethacin and sucrose demonstrate large volume fractions of amorphous material after sufficient plastic deformation, while smaller amorphous volume fractions are predicted in acetaminophen and aspirin, in agreement with experimental observation.

  19. Atomic-scale disproportionation in amorphous silicon monoxide

    NASA Astrophysics Data System (ADS)

    Hirata, Akihiko; Kohara, Shinji; Asada, Toshihiro; Arao, Masazumi; Yogi, Chihiro; Imai, Hideto; Tan, Yongwen; Fujita, Takeshi; Chen, Mingwei

    2016-05-01

    Solid silicon monoxide is an amorphous material which has been commercialized for many functional applications. However, the amorphous structure of silicon monoxide is a long-standing question because of the uncommon valence state of silicon in the oxide. It has been deduced that amorphous silicon monoxide undergoes an unusual disproportionation by forming silicon- and silicon-dioxide-like regions. Nevertheless, the direct experimental observation is still missing. Here we report the amorphous structure characterized by angstrom-beam electron diffraction, supplemented by synchrotron X-ray scattering and computer simulations. In addition to the theoretically predicted amorphous silicon and silicon-dioxide clusters, suboxide-type tetrahedral coordinates are detected by angstrom-beam electron diffraction at silicon/silicon-dioxide interfaces, which provides compelling experimental evidence on the atomic-scale disproportionation of amorphous silicon monoxide. Eventually we develop a heterostructure model of the disproportionated silicon monoxide which well explains the distinctive structure and properties of the amorphous material.

  20. Amorphous-crystalline transition in thermoelectric NbO2

    NASA Astrophysics Data System (ADS)

    Music, Denis; Chen, Yen-Ting; Bliem, Pascal; Geyer, Richard W.

    2015-06-01

    Density functional theory was employed to design enhanced amorphous NbO2 thermoelectrics. The covalent-ionic nature of Nb-O bonding is identical in amorphous NbO2 and its crystalline counterpart. However, the Anderson localisation occurs in amorphous NbO2, which may affect the transport properties. We calculate a multifold increase in the absolute Seebeck coefficient for the amorphous state. These predictions were critically appraised by measuring the Seebeck coefficient of sputtered amorphous and crystalline NbO2 thin films with the identical short-range order. The first-order phase transition occurs at approximately 550 °C, but amorphous NbO2 possesses enhanced transport properties at all temperatures. Amorphous NbO2, reaching  -173 μV K-1, exhibits up to a 29% larger absolute Seebeck coefficient value, thereby validating the predictions.

  1. Atomic-scale disproportionation in amorphous silicon monoxide.

    PubMed

    Hirata, Akihiko; Kohara, Shinji; Asada, Toshihiro; Arao, Masazumi; Yogi, Chihiro; Imai, Hideto; Tan, Yongwen; Fujita, Takeshi; Chen, Mingwei

    2016-05-13

    Solid silicon monoxide is an amorphous material which has been commercialized for many functional applications. However, the amorphous structure of silicon monoxide is a long-standing question because of the uncommon valence state of silicon in the oxide. It has been deduced that amorphous silicon monoxide undergoes an unusual disproportionation by forming silicon- and silicon-dioxide-like regions. Nevertheless, the direct experimental observation is still missing. Here we report the amorphous structure characterized by angstrom-beam electron diffraction, supplemented by synchrotron X-ray scattering and computer simulations. In addition to the theoretically predicted amorphous silicon and silicon-dioxide clusters, suboxide-type tetrahedral coordinates are detected by angstrom-beam electron diffraction at silicon/silicon-dioxide interfaces, which provides compelling experimental evidence on the atomic-scale disproportionation of amorphous silicon monoxide. Eventually we develop a heterostructure model of the disproportionated silicon monoxide which well explains the distinctive structure and properties of the amorphous material.

  2. Characterization of Poly-Amorphous Indomethacin by Terahertz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Otsuka, Makoto; Nishizawa, Jun-ichi; Fukura, Naomi; Sasaki, Tetsuo

    2012-09-01

    Since the stability of amorphous solids of pharmaceuticals differs depending on the method of preparation, there are several solid-state chemical structures in amorphous solids, which like poly-amorphous solids might have different characteristics the same as in crystalline solids. However, it is not easy to identify the differences in solid-state characteristics between amorphous solids using conventional analytical methods, such as powder X-ray diffraction analysis, since all of the poly-amorphous solids had similar halo X-ray diffraction patterns. However, terahertz spectroscopy can distinguish the amorphous solids of indomethacin with different physicochemical properties, and is expected to provide a rapid and non-destructive qualitative analysis for the solid materials, it would be useful for the qualitative evaluation of amorphous solids in the pharmaceutical industry.

  3. Characterization of Poly-Amorphous Indomethacin by Terahertz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Otsuka, Makoto; Nishizawa, Jun-ichi; Fukura, Naomi; Sasaki, Tetsuo

    2012-05-01

    Since the stability of amorphous solids of pharmaceuticals differs depending on the method of preparation, there are several solid-state chemical structures in amorphous solids, which like poly-amorphous solids might have different characteristics the same as in crystalline solids. However, it is not easy to identify the differences in solid-state characteristics between amorphous solids using conventional analytical methods, such as powder X-ray diffraction analysis, since all of the poly-amorphous solids had similar halo X-ray diffraction patterns. However, terahertz spectroscopy can distinguish the amorphous solids of indomethacin with different physicochemical properties, and is expected to provide a rapid and non-destructive qualitative analysis for the solid materials, it would be useful for the qualitative evaluation of amorphous solids in the pharmaceutical industry.

  4. Atomic-scale disproportionation in amorphous silicon monoxide

    PubMed Central

    Hirata, Akihiko; Kohara, Shinji; Asada, Toshihiro; Arao, Masazumi; Yogi, Chihiro; Imai, Hideto; Tan, Yongwen; Fujita, Takeshi; Chen, Mingwei

    2016-01-01

    Solid silicon monoxide is an amorphous material which has been commercialized for many functional applications. However, the amorphous structure of silicon monoxide is a long-standing question because of the uncommon valence state of silicon in the oxide. It has been deduced that amorphous silicon monoxide undergoes an unusual disproportionation by forming silicon- and silicon-dioxide-like regions. Nevertheless, the direct experimental observation is still missing. Here we report the amorphous structure characterized by angstrom-beam electron diffraction, supplemented by synchrotron X-ray scattering and computer simulations. In addition to the theoretically predicted amorphous silicon and silicon-dioxide clusters, suboxide-type tetrahedral coordinates are detected by angstrom-beam electron diffraction at silicon/silicon-dioxide interfaces, which provides compelling experimental evidence on the atomic-scale disproportionation of amorphous silicon monoxide. Eventually we develop a heterostructure model of the disproportionated silicon monoxide which well explains the distinctive structure and properties of the amorphous material. PMID:27172815

  5. Annealing behavior of high permeability amorphous alloys

    SciTech Connect

    Rabenberg, L.

    1980-06-01

    Effects of low temperature annealing on the magnetic properties of the amorphous alloy Co/sub 71/ /sub 4/Fe/sub 4/ /sub 6/Si/sub 9/ /sub 6/B/sub 14/ /sub 4/ were investigated. Annealing this alloy below 400/sup 0/C results in magnetic hardening; annealing above 400/sup 0/C but below the crystallization temperature results in magnetic softening. Above the crystallization temperature the alloy hardens drastically and irreversibly. Conventional and high resolution transmission electron microscopy were used to show that the magnetic property changes at low temperatures occur while the alloy is truly amorphous. By imaging the magnetic microstructures, Lorentz electron microscopy has been able to detect the presence of microscopic inhomogeneities in this alloy. The low temperature annealing behavior of this alloy has been explained in terms of atomic pair ordering in the presence of the internal molecular field. Lorentz electron microscopy has been used to confirm this explanation.

  6. Thermoluminescence characteristics of hydrogenated amorphous zirconia

    NASA Astrophysics Data System (ADS)

    Montalvo, T. R.; Tenorio, L. O.; Nieto, J. A.; Salgado, M. B.; Estrada, A. M. S.; Furetta, C.

    2005-05-01

    This paper reports the experimental results concerning the thermoluminescent (TL) characteristics of hydrogenated amorphous zirconium oxide (a-Zr:H) powder prepared by the sol-gel method. The advantages of this method are the homogeneity and the purity of the gels associated with a relatively low sintering temperature. Hydrogenated amorphous powder was characterized by thermal analysis and X-ray diffraction. The main TL characteristics investigated were the TL response as a function of the absorbed dose, the reproducibility of the TL readings and the fading. The undoped a-Zr:H powder presents a TL glow curve with two peaks centered at 150 and 260 degrees C, respectively, after beta irradiation. The TL response a-Zr:H as a function of the absorbed dose showed a linear behavior over a wide range. The results presented open the possibility to use this material as a good TL dosimeter.

  7. Germanium detector passivated with hydrogenated amorphous germanium

    DOEpatents

    Hansen, William L.; Haller, Eugene E.

    1986-01-01

    Passivation of predominantly crystalline semiconductor devices (12) is provided for by a surface coating (21) of sputtered hydrogenated amorphous semiconductor material. Passivation of a radiation detector germanium diode, for example, is realized by sputtering a coating (21) of amorphous germanium onto the etched and quenched diode surface (11) in a low pressure atmosphere of hydrogen and argon. Unlike prior germanium diode semiconductor devices (12), which must be maintained in vacuum at cryogenic temperatures to avoid deterioration, a diode processed in the described manner may be stored in air at room temperature or otherwise exposed to a variety of environmental conditions. The coating (21) compensates for pre-existing undesirable surface states as well as protecting the semiconductor device (12) against future impregnation with impurities.

  8. Wear Resistant Amorphous and Nanocomposite Coatings

    SciTech Connect

    Racek, O

    2008-03-26

    Glass forming materials (critical cooling rate <10{sup 4}K.s{sup -1}) are promising for their high corrosion and wear resistance. During rapid cooling, the materials form an amorphous structure that transforms to nanocrystalline during a process of devitrification. High hardness (HV 1690) can be achieved through a controlled crystallization. Thermal spray process has been used to apply coatings, which preserves the amorphous/nanocomposite structure due to a high cooling rate of the feedstock particles during the impact on a substrate. Wear properties have been studied with respect to process conditions and feedstock material properties. Application specific properties such as sliding wear resistance have been correlated with laboratory tests based on instrumented indentation and scratch tests.

  9. Characterization of Amorphous Zinc Tin Oxide Semiconductors

    SciTech Connect

    Rajachidambaram, Jaana Saranya; Sanghavi, Shail P.; Nachimuthu, Ponnusamy; Shutthanandan, V.; Varga, Tamas; Flynn, Brendan T.; Thevuthasan, Suntharampillai; Herman, Gregory S.

    2012-06-12

    Amorphous zinc tin oxide (ZTO) was investigated to determine the effect of deposition and post annealing conditions on film structure, composition, surface contamination, and thin film transistor (TFT) device performance. X-ray diffraction results indicated that the ZTO films remain amorphous even after annealing to 600 °C. We found that the bulk Zn:Sn ratio of the sputter deposited films were slightly tin rich compared to the composition of the ceramic sputter target, and there was a significant depletion of zinc at the surface. X-ray photoelectron spectroscopy also indicated that residual surface contamination depended strongly on the sample post-annealing conditions where water, carbonate and hydroxyl species were absorbed to the surface. Electrical characterization of ZTO films, using TFT test structures, indicated that mobilities as high as 17 cm2/Vs could be obtained for depletion mode devices.

  10. Reversibility and criticality in amorphous solids

    PubMed Central

    Regev, Ido; Weber, John; Reichhardt, Charles; Dahmen, Karin A.; Lookman, Turab

    2015-01-01

    The physical processes governing the onset of yield, where a material changes its shape permanently under external deformation, are not yet understood for amorphous solids that are intrinsically disordered. Here, using molecular dynamics simulations and mean-field theory, we show that at a critical strain amplitude the sizes of clusters of atoms undergoing cooperative rearrangements of displacements (avalanches) diverges. We compare this non-equilibrium critical behaviour to the prevailing concept of a ‘front depinning' transition that has been used to describe steady-state avalanche behaviour in different materials. We explain why a depinning-like process can result in a transition from periodic to chaotic behaviour and why chaotic motion is not possible in pinned systems. These findings suggest that, at least for highly jammed amorphous systems, the irreversibility transition may be a side effect of depinning that occurs in systems where the disorder is not quenched. PMID:26564783

  11. Reversibility and criticality in amorphous solids

    DOE PAGES

    Regev, Ido; Weber, John; Reichhardt, Charles; Dahmen, Karin A.; Lookman, Turab

    2015-11-13

    The physical processes governing the onset of yield, where a material changes its shape permanently under external deformation, are not yet understood for amorphous solids that are intrinsically disordered. Here, using molecular dynamics simulations and mean-field theory, we show that at a critical strain amplitude the sizes of clusters of atoms undergoing cooperative rearrangements of displacements (avalanches) diverges. We compare this non-equilibrium critical behaviour to the prevailing concept of a ‘front depinning’ transition that has been used to describe steady-state avalanche behaviour in different materials. We explain why a depinning-like process can result in a transition from periodic to chaoticmore » behaviour and why chaotic motion is not possible in pinned systems. As a result, these findings suggest that, at least for highly jammed amorphous systems, the irreversibility transition may be a side effect of depinning that occurs in systems where the disorder is not quenched.« less

  12. Reversibility and criticality in amorphous solids

    SciTech Connect

    Regev, Ido; Weber, John; Reichhardt, Charles; Dahmen, Karin A.; Lookman, Turab

    2015-11-13

    The physical processes governing the onset of yield, where a material changes its shape permanently under external deformation, are not yet understood for amorphous solids that are intrinsically disordered. Here, using molecular dynamics simulations and mean-field theory, we show that at a critical strain amplitude the sizes of clusters of atoms undergoing cooperative rearrangements of displacements (avalanches) diverges. We compare this non-equilibrium critical behaviour to the prevailing concept of a ‘front depinning’ transition that has been used to describe steady-state avalanche behaviour in different materials. We explain why a depinning-like process can result in a transition from periodic to chaotic behaviour and why chaotic motion is not possible in pinned systems. As a result, these findings suggest that, at least for highly jammed amorphous systems, the irreversibility transition may be a side effect of depinning that occurs in systems where the disorder is not quenched.

  13. Reversibility and criticality in amorphous solids.

    PubMed

    Regev, Ido; Weber, John; Reichhardt, Charles; Dahmen, Karin A; Lookman, Turab

    2015-01-01

    The physical processes governing the onset of yield, where a material changes its shape permanently under external deformation, are not yet understood for amorphous solids that are intrinsically disordered. Here, using molecular dynamics simulations and mean-field theory, we show that at a critical strain amplitude the sizes of clusters of atoms undergoing cooperative rearrangements of displacements (avalanches) diverges. We compare this non-equilibrium critical behaviour to the prevailing concept of a 'front depinning' transition that has been used to describe steady-state avalanche behaviour in different materials. We explain why a depinning-like process can result in a transition from periodic to chaotic behaviour and why chaotic motion is not possible in pinned systems. These findings suggest that, at least for highly jammed amorphous systems, the irreversibility transition may be a side effect of depinning that occurs in systems where the disorder is not quenched. PMID:26564783

  14. Design Requirements for Amorphous Piezoelectric Polymers

    NASA Technical Reports Server (NTRS)

    Ounaies, Z.; Young, J. A.; Harrison, J. S.

    1999-01-01

    An overview of the piezoelectric activity in amorphous piezoelectric polymers is presented. The criteria required to render a polymer piezoelectric are discussed. Although piezoelectricity is a coupling between mechanical and electrical properties, most research has concentrated on the electrical properties of potentially piezoelectric polymers. In this work, we present comparative mechanical data as a function of temperature and offer a summary of polarization and electromechanical properties for each of the polymers considered.

  15. Synthesis of new amorphous metallic spin glasses

    DOEpatents

    Haushalter, R.C.

    1985-02-11

    Disclosed are: amorphous metallic precipitates having the formula (M/sub 1/)/sub a/(M/sub 2/)/sub b/ wherein M/sub 1/ is at least one transition metal, M/sub 2/ is at least one main group metal and the integers ''a'' and ''b'' provide stoichiometric balance; the precipitates having a degree of local order characteristic of chemical compounds from the precipitation process and useful electrical and mechanical properties.

  16. Synthesis of new amorphous metallic spin glasses

    DOEpatents

    Haushalter, Robert C.

    1988-01-01

    Amorphous metallic precipitates having the formula (M.sub.1).sub.a (M.sub.2).sub.b wherein M.sub.1 is at least one transition metal, M.sub.2 is at least one main group metal and the integers "a" and "b" provide stoichiometric balance; the precipitates having a degree of local order characteristic of chemical compounds from the precipitation process and useful electrical and mechanical properties.

  17. Synthesis of new amorphous metallic spin glasses

    DOEpatents

    Haushalter, Robert C.

    1986-01-01

    Amorphous metallic precipitates having the formula (M.sub.1).sub.a (M.sub.2).sub.b wherein M.sub.1 is at least one transition metal, M.sub.2 is at least one main group metal and the integers "a" and "b" provide stoichiometric balance; the precipitates having a degree of local order characteristic of chemical compounds from the precipitation process and useful electrical and mechanical properties.

  18. Multiple cell photoresponsive amorphous alloys and devices

    SciTech Connect

    Ovshinsky, S.R.; Adler, D.

    1990-01-02

    This patent describes an improved photoresponsive tandem multiple solar cell device. The device comprising: at least a first and second superimposed cell of various materials. The first cell being formed of a silicon alloy material. The second cell including an amorphous silicon alloy semiconductor cell body having an active photoresponsive region in which radiation can impinge to produce charge carriers, the amorphous cell body including at least one density of states reducing element. The element being fluorine. The amorphous cell body further including a band gap adjusting element therein at least in the photoresponsive region to enhance the radiation absorption thereof, the adjusting element being germanium: the second cell being a multi-layer body having deposited semiconductor layers of opposite (p and n) conductivity type; and the first cell being formed with the second cell in substantially direct Junction contact therebetween. The first and second cells designed to generate substantially matched currents from each cell from a light source directed through the first cell and into the second cell.

  19. Concurrent multiscale modeling of amorphous materials

    NASA Astrophysics Data System (ADS)

    Tan, Vincent

    2013-03-01

    An approach to multiscale modeling of amorphous materials is presented whereby atomistic scale domains coexist with continuum-like domains. The atomistic domains faithfully predict severe deformation while the continuum domains allow the computation to scale up the size of the model without incurring excessive computational costs associated with fully atomistic models and without the introduction of spurious forces across the boundary of atomistic and continuum-like domains. The material domain is firstly constructed as a tessellation of Amorphous Cells (AC). For regions of small deformation, the number of degrees of freedom is then reduced by computing the displacements of only the vertices of the ACs instead of the atoms within. This is achieved by determining, a priori, the atomistic displacements within such Pseudo Amorphous Cells associated with orthogonal deformation modes of the cell. Simulations of nanoscale polymer tribology using full molecular mechanics computation and our multiscale approach give almost identical prediction of indentation force and the strain contours of the polymer. We further demonstrate the capability of performing adaptive simulations during which domains that were discretized into cells revert to full atomistic domains when their strain attain a predetermined threshold. The authors would like to acknowledge the financial support given to this study by the Agency of Science, Technology and Research (ASTAR), Singapore (SERC Grant No. 092 137 0013).

  20. Phase transitions in biogenic amorphous calcium carbonate

    NASA Astrophysics Data System (ADS)

    Gong, Yutao

    Geological calcium carbonate exists in both crystalline phases and amorphous phases. Compared with crystalline calcium carbonate, such as calcite, aragonite and vaterite, the amorphous calcium carbonate (ACC) is unstable. Unlike geological calcium carbonate crystals, crystalline sea urchin spicules (99.9 wt % calcium carbonate and 0.1 wt % proteins) do not present facets. To explain this property, crystal formation via amorphous precursors was proposed in theory. And previous research reported experimental evidence of ACC on the surface of forming sea urchin spicules. By using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy (PEEM), we studied cross-sections of fresh sea urchin spicules at different stages (36h, 48h and 72h after fertilization) and observed the transition sequence of three mineral phases: hydrated ACC → dehydrated ACC → biogenic calcite. In addition, we unexpectedly found hydrated ACC nanoparticles that are surrounded by biogenic calcite. This observation indicates the dehydration from hydrated ACC to dehydrated ACC is inhibited, resulting in stabilization of hydrated ACC nanoparticles. We thought that the dehydration was inhibited by protein matrix components occluded within the biomineral, and we designed an in vitro assay to test the hypothesis. By utilizing XANES-PEEM, we found that SM50, the most abundant occluded matrix protein in sea urchin spicules, has the function to stabilize hydrated ACC in vitro.

  1. Amorphous molybdenum silicon superconducting thin films

    SciTech Connect

    Bosworth, D. Sahonta, S.-L.; Barber, Z. H.; Hadfield, R. H.

    2015-08-15

    Amorphous superconductors have become attractive candidate materials for superconducting nanowire single-photon detectors due to their ease of growth, homogeneity and competitive superconducting properties. To date the majority of devices have been fabricated using W{sub x}Si{sub 1−x}, though other amorphous superconductors such as molybdenum silicide (Mo{sub x}Si{sub 1−x}) offer increased transition temperature. This study focuses on the properties of MoSi thin films grown by magnetron sputtering. We examine how the composition and growth conditions affect film properties. For 100 nm film thickness, we report that the superconducting transition temperature (Tc) reaches a maximum of 7.6 K at a composition of Mo{sub 83}Si{sub 17}. The transition temperature and amorphous character can be improved by cooling of the substrate during growth which inhibits formation of a crystalline phase. X-ray diffraction and transmission electron microscopy studies confirm the absence of long range order. We observe that for a range of 6 common substrates (silicon, thermally oxidized silicon, R- and C-plane sapphire, x-plane lithium niobate and quartz), there is no variation in superconducting transition temperature, making MoSi an excellent candidate material for SNSPDs.

  2. Amorphous molybdenum silicon superconducting thin films

    NASA Astrophysics Data System (ADS)

    Bosworth, D.; Sahonta, S.-L.; Hadfield, R. H.; Barber, Z. H.

    2015-08-01

    Amorphous superconductors have become attractive candidate materials for superconducting nanowire single-photon detectors due to their ease of growth, homogeneity and competitive superconducting properties. To date the majority of devices have been fabricated using WxSi1-x, though other amorphous superconductors such as molybdenum silicide (MoxSi1-x) offer increased transition temperature. This study focuses on the properties of MoSi thin films grown by magnetron sputtering. We examine how the composition and growth conditions affect film properties. For 100 nm film thickness, we report that the superconducting transition temperature (Tc) reaches a maximum of 7.6 K at a composition of Mo83Si17. The transition temperature and amorphous character can be improved by cooling of the substrate during growth which inhibits formation of a crystalline phase. X-ray diffraction and transmission electron microscopy studies confirm the absence of long range order. We observe that for a range of 6 common substrates (silicon, thermally oxidized silicon, R- and C-plane sapphire, x-plane lithium niobate and quartz), there is no variation in superconducting transition temperature, making MoSi an excellent candidate material for SNSPDs.

  3. Characterization of Amorphous and Co-Amorphous Simvastatin Formulations Prepared by Spray Drying.

    PubMed

    Craye, Goedele; Löbmann, Korbinian; Grohganz, Holger; Rades, Thomas; Laitinen, Riikka

    2015-01-01

    In this study, spray drying from aqueous solutions, using the surface-active agent sodium lauryl sulfate (SLS) as a solubilizer, was explored as a production method for co-amorphous simvastatin-lysine (SVS-LYS) at 1:1 molar mixtures, which previously have been observed to form a co-amorphous mixture upon ball milling. In addition, a spray-dried formulation of SVS without LYS was prepared. Energy-dispersive X-ray spectroscopy (EDS) revealed that SLS coated the SVS and SVS-LYS particles upon spray drying. X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC) showed that in the spray-dried formulations the remaining crystallinity originated from SLS only. The best dissolution properties and a "spring and parachute" effect were found for SVS spray-dried from a 5% SLS solution without LYS. Despite the presence of at least partially crystalline SLS in the mixtures, all the studied formulations were able to significantly extend the stability of amorphous SVS compared to previous co-amorphous formulations of SVS. The best stability (at least 12 months in dry conditions) was observed when SLS was spray-dried with SVS (and LYS). In conclusion, spray drying of SVS and LYS from aqueous surfactant solutions was able to produce formulations with improved physical stability for amorphous SVS. PMID:26633346

  4. Characterizing Amorphous Silicates in Extraterrestrial Materials

    NASA Astrophysics Data System (ADS)

    Fu, X.; Wang, A.; Krawczynski, M. J.

    2015-12-01

    Amorphous silicates are common in extraterrestrial materials. They are seen in the matrix of carbonaceous chondrites as well as in planetary materials. Tagish Lake is one of the most primitive carbonaceous meteorites in which TEM and XRD analyses found evidence for poorly crystalline phyllosilicate-like species; Raman spectra revealed amorphous silicates with variable degree of polymerization and low crystallinity. On Mars, CheMin discovered amorphous phases in all analyzed samples, and poorly crystalline smectite in mudstone samples. These discoveries pose questions on the crystallinity of phyllosilicates found by remote sensing on Mars, which is directly relevant to aqueous alteration during geologic history of Mars. Our goal is to use spectroscopy to better characterize amorphous silicates. We use three approaches: (1) using silicate glasses synthesized with controlled chemistry to study the effects of silicate polymerization and (2) using phyllosilicates synthesized with controlled hydrothermal treatment to study the effect of crystallinity on vibrational spectroscopy, finally (3) to use the developed correlations in above two steps to study amorphous phases in meteorites, and those found in future missions to Mars. In the 1st step, silicate glasses were synthesized from pure oxides in a range of NBO/T ratios (from 0 to 4). Depending on the targeted NBO/T and composition of mixed oxides, temperatures for each experiment fell in a range from 1260 to 1520 °C, run for ~ 4 hrs. The melt was quenched in liquid N2 or water. Homogeneity of glass was checked under optical microscopy. Raman spectra were taken over 100 spots on small chips free of bubbles and crystals. We have observed that accompanying an increase of NBO/T, there is a strengthening and a position shift of the Raman peak near 1000 cm-1 (Si-Onon-bridging stretching mode), and the weakening of broad Raman peaks near 500 cm-1 (ring breathing mode) and 700cm-1 (Si-Obridging-Si mode). We are building the

  5. Infrared emission from hydrogenated amorphous carbon and amorphous carbon grains in the interstellar medium

    NASA Technical Reports Server (NTRS)

    Duley, W. W.; Jones, A. P.; Taylor, S. D.; Williams, D. A.

    1993-01-01

    The correlations deduced by Boulanger et al. (1990) from IRAS maps of the Chamaeleon, Taurus and Ursa Major molecular cloud complexes are interpreted in terms of the evolutionary hydrogenated amorphous carbon model of interstellar dust. In particular, regions of relatively strong 12-micron emission may be regions where recently accreted carbon is being converted by ambient UV to small PAHs in situ. Regions of weak 12-micron emission are probably quiescent regions where carbon has been annealed to amorphous carbon. Observational consequences of these inferences are briefly described.

  6. Formation of amorphous silicon by light ion damage

    SciTech Connect

    Shih, Y.C.

    1985-12-01

    Amorphization by implantation of boron ions (which is the lightest element generally used in I.C. fabrication processes) has been systematically studied for various temperatures, various voltages and various dose rates. Based on theoretical considerations and experimental results, a new amorphization model for light and intermediate mass ion damage is proposed consisting of two stages. The role of interstitial type point defects or clusters in amorphization is emphasized. Due to the higher mobility of interstitials out-diffusion to the surface particularly during amorphization with low energy can be significant. From a review of the idealized amorphous structure, diinterstitial-divacancy pairs are suggested to be the embryos of amorphous zones formed during room temperature implantation. The stacking fault loops found in specimens implanted with boron at room temperature are considered to be the origin of secondary defects formed during annealing.

  7. Amorphous silicon/polycrystalline thin film solar cells

    SciTech Connect

    Ullal, H.S.

    1991-03-13

    An improved photovoltaic solar cell is described including a p-type amorphous silicon layer, intrinsic amorphous silicon, and an n-type polycrystalline semiconductor such as cadmium sulfide, cadmium zinc sulfide, zinc selenide, gallium phosphide, and gallium nitride. The polycrystalline semiconductor has an energy bandgap greater than that of the amorphous silicon. The solar cell can be provided as a single-junction device or a multijunction device.

  8. Structure and dynamics of amorphous water ice.

    PubMed

    Laufer, D; Kochavi, E; Bar-Nun, A

    1987-12-15

    Further insight into the structure and dynamics of amorphous water ice, at low temperatures, was obtained by trapping in it Ar, Ne, H2, and D2. Ballistic water-vapor deposition results in the growth of smooth, approximately 1 x 0.2 micrometer2, ice needles. The amorphous ice seems to exist in at least two separate forms, at T < 85 K and at 85 < T < 136.8 K, and transform irreversibly from one form to the other through a series of temperature-dependent metastable states. The channels formed by the water hexagons in the ice are wide enough to allow the free penetration of H2 and D2 into the ice matrix even in the relatively compact cubic ice, resulting in H2-(D2-) to-ice ratios (by number) as high as 0.63. The larger Ar atoms can penetrate only into the wider channels of amorphous ice, and Ne is an intermediate case. Dynamic percolation behavior explains the emergence of Ar and Ne (but not H2 and D2) for the ice, upon warming, in small and big gas jets. The big jets, each containing approximately 5 x 10(10) atoms, break and propel the ice needles. Dynamic percolation also explains the collapse of the ice matrix under bombardment by Ar , at a pressure exceeding 2.6 dyn cm-2, and the burial of huge amounts of gas inside the collapsed matrix, up to an Ar-to-ice of 3.3 (by number). The experimental results could be relevant to comets, icy satellites, and icy grain mantles in dense interstellar clouds.

  9. Structure and dynamics of amorphous water ice

    NASA Technical Reports Server (NTRS)

    Laufer, D.; Kochavi, E.; Bar-Nun, A.; Owen, T. (Principal Investigator)

    1987-01-01

    Further insight into the structure and dynamics of amorphous water ice, at low temperatures, was obtained by trapping in it Ar, Ne, H2, and D2. Ballistic water-vapor deposition results in the growth of smooth, approximately 1 x 0.2 micrometer2, ice needles. The amorphous ice seems to exist in at least two separate forms, at T < 85 K and at 85 < T < 136.8 K, and transform irreversibly from one form to the other through a series of temperature-dependent metastable states. The channels formed by the water hexagons in the ice are wide enough to allow the free penetration of H2 and D2 into the ice matrix even in the relatively compact cubic ice, resulting in H2-(D2-) to-ice ratios (by number) as high as 0.63. The larger Ar atoms can penetrate only into the wider channels of amorphous ice, and Ne is an intermediate case. Dynamic percolation behavior explains the emergence of Ar and Ne (but not H2 and D2) for the ice, upon warming, in small and big gas jets. The big jets, each containing approximately 5 x 10(10) atoms, break and propel the ice needles. Dynamic percolation also explains the collapse of the ice matrix under bombardment by Ar , at a pressure exceeding 2.6 dyn cm-2, and the burial of huge amounts of gas inside the collapsed matrix, up to an Ar-to-ice of 3.3 (by number). The experimental results could be relevant to comets, icy satellites, and icy grain mantles in dense interstellar clouds.

  10. Medical imaging applications of amorphous silicon

    SciTech Connect

    Mireshghi, A.; Drewery, J.S.; Hong, W.S.; Jing, T.; Kaplan, S.N.; Lee, H.K.; Perez-Mendez, V.

    1994-07-01

    Two dimensional hydrogenated amorphous silicon (a-Si:H) pixel arrays are good candidates as flat-panel imagers for applications in medical imaging. Various performance characteristics of these imagers are reviewed and compared with currently used equipments. An important component in the a-Si:H imager is the scintillator screen. A new approach for fabrication of high resolution CsI(Tl) scintillator layers, appropriate for coupling to a-Si:H arrays, are presented. For nuclear medicine applications, a new a-Si:H based gamma camera is introduced and Monte Carlo simulation is used to evaluate its performance.

  11. Radiation resistance studies of amorphous silicon films

    NASA Technical Reports Server (NTRS)

    Woodyard, James R.; Payson, J. Scott

    1989-01-01

    Hydrogenated amorphous silicon thin films were irradiated with 2.00 MeV helium ions using fluences ranging from 1E11 to 1E15 cm(-2). The films were characterized using photothermal deflection spectroscopy and photoconductivity measurements. The investigations show that the radiation introduces sub-band-gap states 1.35 eV below the conduction band and the states increase supralinearly with fluence. Photoconductivity measurements suggest the density of states above the Fermi energy is not changing drastically with fluence.

  12. Mechanism for hydrogen diffusion in amorphous silicon

    SciTech Connect

    Biswas, R.; Li, Q.; Pan, B.C.; Yoon, Y.

    1998-01-01

    Tight-binding molecular-dynamics calculations reveal a mechanism for hydrogen diffusion in hydrogenated amorphous silicon. Hydrogen diffuses through the network by successively bonding with nearby silicons and breaking their Si{endash}Si bonds. The diffusing hydrogen carries with it a newly created dangling bond. These intermediate transporting states are densely populated in the network, have lower energies than H at the center of stretched Si{endash}Si bonds, and can play a crucial role in hydrogen diffusion. {copyright} {ital 1998} {ital The American Physical Society}

  13. Obstacles using amorphous materials for volume applications

    NASA Astrophysics Data System (ADS)

    Kiessling, Albert; Reininger, Thomas

    2012-10-01

    This contribution is especially focussed on the attempt to use amorphous or nanocrystalline metals in position sensor applications and to describe the difficulties and obstacles encountered in coherence with the development of appropriate industrial high volume series products in conjunction with the related quality requirements. The main motivation to do these investigations was to beat the generally known sensors especially silicon based Hall-sensors as well as AMR- and GMR-sensors - well known from mobile phones and electronic storage devices like hard discs and others - in terms of cost-effectiveness and functionality.

  14. Amorphous computing: examples, mathematics and theory.

    PubMed

    Stark, W Richard

    2013-01-01

    The cellular automata model was described by John von Neumann and his friends in the 1950s as a representation of information processing in multicellular tissue. With crystalline arrays of cells and synchronous activity, it missed the mark (Stark and Hughes, BioSystems 55:107-117, 2000). Recently, amorphous computing, a valid model for morphogenesis in multicellular information processing, has begun to fill the void. Through simple examples and elementary mathematics, this paper begins a computation theory for this important new direction. PMID:23946719

  15. Diffusion and ion mixing in amorphous alloys

    SciTech Connect

    Hahn, H.; Averback, R.S.; Ding, F.; Loxton, C.; Baker, J.

    1986-10-01

    Tracer impurity diffusion and ion beam mixing in amorphous (a-)Ni/sub 50/Zr/sub 50/ were measured. A correlation between the metallic radius of an impurity and its tracer diffusivity was observed; it is similar to that found in crystalline ..cap alpha..-Zr and ..cap alpha..-Ti. In addition, the temperature dependence of diffusion in a-NiZr exhibits Arrhenius behavior. Ion beam mixing of different impurities in a-NiZr correlates with tracer diffusivity at both high and low temperatures. At higher temperatures radiation enhanced diffusion (RED) was observed. The activation enthalpy of the RED diffusion coefficient is 0.3 eV/atom.

  16. Encoding of Memory in Sheared Amorphous Solids

    NASA Astrophysics Data System (ADS)

    Fiocco, Davide; Foffi, Giuseppe; Sastry, Srikanth

    2014-01-01

    We show that memory can be encoded in a model amorphous solid subjected to athermal oscillatory shear deformations, and in an analogous spin model with disordered interactions, sharing the feature of a deformable energy landscape. When these systems are subjected to oscillatory shear deformation, they retain memory of the deformation amplitude imposed in the training phase, when the amplitude is below a "localization" threshold. Remarkably, multiple persistent memories can be stored using such an athermal, noise-free, protocol. The possibility of such memory is shown to be linked to the presence of plastic deformations and associated limit cycles traversed by the system, which exhibit avalanche statistics also seen in related contexts.

  17. Self-Diffusion in Amorphous Silicon.

    PubMed

    Strauß, Florian; Dörrer, Lars; Geue, Thomas; Stahn, Jochen; Koutsioubas, Alexandros; Mattauch, Stefan; Schmidt, Harald

    2016-01-15

    The present Letter reports on self-diffusion in amorphous silicon. Experiments were done on ^{29}Si/^{nat}Si heterostructures using neutron reflectometry and secondary ion mass spectrometry. The diffusivities follow the Arrhenius law in the temperature range between 550 and 700 °C with an activation energy of (4.4±0.3)  eV. In comparison with single crystalline silicon the diffusivities are tremendously higher by 5 orders of magnitude at about 700 °C, which can be interpreted as the consequence of a high diffusion entropy. PMID:26824552

  18. Deuterium in crystalline and amorphous silicon

    SciTech Connect

    Borzi, R.; Ma, H.; Fedders, P.A.; Leopold, D.J.; Norberg, R.E.; Boyce, J.B.; Johnson, N.M.; Ready, S.E.; Walker, J.

    1997-07-01

    The authors report deuteron magnetic resonance (DMR) measurements on aged deuterium-implanted single crystal n-type silicon and comparisons with amorphous silicon spectra. The sample film was prepared six years ago by deuteration from a-D{sub 2} plasma and evaluated by a variety of experimental methods. Deuterium has been evolving with time and the present DMR signal shows a smaller deuteron population. A doublet from Si-D configurations along (111) has decreased more than have central molecular DMR components, which include 47 and 12 kHz FWHM gaussians. Transient DMR magnetization recoveries indicate spin lattice relaxation to para-D{sub 2} relaxation centers.

  19. Cyclic behaviors of amorphous shape memory polymers.

    PubMed

    Yu, Kai; Li, Hao; McClung, Amber J W; Tandon, Gyaneshwar P; Baur, Jeffery W; Qi, H Jerry

    2016-04-01

    Cyclic loading conditions are commonly encountered in the applications of shape memory polymers (SMPs), where the cyclic characteristics of the materials determine their performance during the service life, such as deformation resistance, shape recovery speed and shape recovery ratio. Recent studies indicate that in addition to the physical damage or some other irreversible softening effects, the viscoelastic nature could also be another possible reason for the degraded cyclic behavior of SMPs. In this paper, we explore in detail the influence of the viscoelastic properties on the cyclic tension and shape memory (SM) behavior of an epoxy based amorphous thermosetting polymer. Cyclic experiments were conducted first, which show that although the epoxy material does not have any visible damage or irreversible softening effect during deformation, it still exhibits obvious degradation in the cyclic tension and SM behaviors. A linear multi-branched model is utilized to assist in the prediction and understanding of the mechanical responses of amorphous SMPs. Parametric studies based on the applied model suggest that the shape memory performance can be improved by adjusting programming and recovery conditions, such as lowering the loading rate, increasing the programming temperature, and reducing the holding time. PMID:26924339

  20. Structural and Elastic Properties of Amorphous Silicon

    NASA Astrophysics Data System (ADS)

    Feldman, Joseph; Papaconstantopoulos, Dimitris; Bernstein, Noam; Mehl, Michael

    2003-03-01

    In this work we study the elastic and structural properties of amorphous silicon using the NRL tight-binding method (N. Bernstein, et al., Phys. Rev. B 62, 4477 (2000).). Using conjugate gradient energy minimization we have relaxed a 216 atom model. The amorphous-crystal energy difference is 0.017 Ryd/atom, similar to a calculation on a related model using the empirical Stillinger-Weber potential and twice the experimental value. The structure of the relaxed model is consistent with diffraction experiments as well as more indirect experimental results. The model is fully four-fold coordinated with an RMS bond angle deviation of only 11^rc, and is expanded 2% in volume with respect to the TB crystalline value. Using the method of homogeneous deformation we have found a relaxed shear modulus of ˜57 GPa (with an estimated 2% uncertainty due to anisotropy) and relaxed bulk modulus of 87.3 GPa, in very good agreement with a previous (ab initio) calculated value of 82.5 GPa (M. Durandurdu and D. A. Drabold, Phys. Rev. B 64, 014101 (2001).). We find that the distribution of relaxation displacements under shear is markedly skewed towards large values. Finally, we discuss the force constants and vacancy energy distributions for several models.

  1. Modeling of amorphous polyaniline emeraldine base.

    PubMed

    Canales, Manel; Curcó, David; Alemán, Carlos

    2010-08-01

    Amorphous polyaniline emeraldine base has been investigated using atomistic classical molecular dynamics simulations. Initially, different sets of force-field parameters, which differ in the atomic charges and/or the van der Waals parameters, were tested. The experimental density of polyaniline was satisfactorily reproduced using the following combination: (i) equilibrium bond lengths, equilibrium bond angles, and electrostatic charges derived from quantum mechanical calculations and (ii) van der Waals parameters extrapolated from GROMOS for all atoms with the exception of the CH pseudoparticles of the phenyl ring, which were taken from an anisotropic united atom potential. Next, this force field was used to investigate the structure of the polymer in the amorphous state, the trajectories performed for this purpose allowing accumulation of 750 ns. Analyses of the energies evidence that the interactions between one repeating unit containing an amine nitrogen atom and another unit with an imine nitrogen are favored with respect to those between two identical repeating units. This conclusion is also supported by quantum mechanical and quantum mechanical/molecular mechanics calculations. On the other hand, the partial radial distribution functions indicate that this material only exhibits short-range intramolecular correlation, which is in excellent agreement with experimental evidence.

  2. Atomic-Scale Imprinting into Amorphous Metals

    NASA Astrophysics Data System (ADS)

    Schwarz, Udo; Li, Rui; Simon, Georg; Kinser, Emely; Liu, Ze; Chen, Zheng; Zhou, Chao; Singer, Jonathan; Osuji, Chinedum; Schroers, Jan

    Nanoimprinting by thermoplastic forming (TPF) has attracted significant attention in recent years due to its promise of low-cost fabrication of nanostructured devices. Usually performed using polymers, amorphous metals have been identified as a material class that might be even better suited for nanoimprinting due to a combination of mechanical properties and processing ability. Commonly referred to as metallic glasses, their featureless atomic structure suggests that there may not be an intrinsic size limit to the material's ability to replicate a mold. To study this hypothesis, we demonstrate atomic-scale imprinting into amorphous metals by TPF under ambient conditions. Atomic step edges of a SrTiO3 (STO) single crystal used as mold were successfully imprinted into Pt-based bulk metallic glasses (BMGs) with high fidelity. Terraces on the BMG replicas possess atomic smoothness with sub-Angstrom roughness that is identical to the one measured on the STO mold. Systematic studies revealed that the quality of the replica depends on the loading rate during imprinting, that the same mold can be used multiple times without degradation of mold or replicas, and that the atomic-scale features on as-imprinted BMG surfaces has impressive long-term stability (months).

  3. Structural Characteristics of Synthetic Amorphous Calcium Carbonate

    SciTech Connect

    Michel, F. Marc; MacDonald, Jason; Feng, Jian; Phillips, Brian L.; Ehm, Lars; Tarabrella, Cathy; Parise, John B.; Reeder, Richard J.

    2008-08-06

    Amorphous calcium carbonate (ACC) is an important phase involved in calcification by a wide variety of invertebrate organisms and is of technological interest in the development of functional materials. Despite widespread scientific interest in this phase a full characterization of structure is lacking. This is mainly due to its metastability and difficulties in evaluating structure using conventional structure determination methods. Here we present new findings from the application of two techniques, pair distribution function analysis and nuclear magnetic resonance spectroscopy, which provide new insight to structural aspects of synthetic ACC. Several important results have emerged from this study of ACC formed in vitro using two common preparation methods: (1) ACC exhibits no structural coherence over distances > 15 {angstrom} and is truly amorphous; (2) most of the hydrogen in ACC is present as structural H{sub 2}O, about half of which undergoes restricted motion on the millisecond time scale near room temperature; (3) the short- and intermediate-range structure of ACC shows no distinct match to any known structure in the calcium carbonate system; and (4) most of the carbonate in ACC is monodentate making it distinctly different from monohydrocalcite. Although the structure of synthetic ACC is still not fully understood, the results presented provide an important baseline for future experiments evaluating biogenic ACC and samples containing certain additives that may play a role in stabilization of ACC, crystallization kinetics, and final polymorph selection.

  4. The future of amorphous silicon photovoltaic technology

    SciTech Connect

    Crandall, R; Luft, W

    1995-06-01

    Amorphous silicon modules are commercially available. They are the first truly commercial thin-film photovoltaic (PV) devices. Well-defined production processes over very large areas (>1 m{sup 2}) have been implemented. There are few environmental issues during manufacturing, deployment in the field, or with the eventual disposal of the modules. Manufacturing safety issues are well characterized and controllable. The highest measured initial efficiency to date is 13.7% for a small triple-stacked cell and the highest stabilized module efficiency is 10%. There is a consensus among researchers, that in order to achieve a 15% stabilized efficiency, a triple-junction amorphous silicon structure is required. Fundamental improvements in alloys are needed for higher efficiencies. This is being pursued through the DOE/NREL Thin-Film Partnership Program. Cost reductions through improved manufacturing processes are being pursued under the National Renewable Energy Laboratory/US Department of Energy (NREL/DOE)-sponsored research in manufacturing technology (PVMaT). Much of the work in designing a-Si devices is a result of trying to compensate for the Staebler-Wronski effect. Some new deposition techniques hold promise because they have produced materials with lower stabilized defect densities. However, none has yet produced a high efficiency device and shown it to be more stable than those from standard glow discharge deposited material.

  5. Cyclic behaviors of amorphous shape memory polymers.

    PubMed

    Yu, Kai; Li, Hao; McClung, Amber J W; Tandon, Gyaneshwar P; Baur, Jeffery W; Qi, H Jerry

    2016-04-01

    Cyclic loading conditions are commonly encountered in the applications of shape memory polymers (SMPs), where the cyclic characteristics of the materials determine their performance during the service life, such as deformation resistance, shape recovery speed and shape recovery ratio. Recent studies indicate that in addition to the physical damage or some other irreversible softening effects, the viscoelastic nature could also be another possible reason for the degraded cyclic behavior of SMPs. In this paper, we explore in detail the influence of the viscoelastic properties on the cyclic tension and shape memory (SM) behavior of an epoxy based amorphous thermosetting polymer. Cyclic experiments were conducted first, which show that although the epoxy material does not have any visible damage or irreversible softening effect during deformation, it still exhibits obvious degradation in the cyclic tension and SM behaviors. A linear multi-branched model is utilized to assist in the prediction and understanding of the mechanical responses of amorphous SMPs. Parametric studies based on the applied model suggest that the shape memory performance can be improved by adjusting programming and recovery conditions, such as lowering the loading rate, increasing the programming temperature, and reducing the holding time.

  6. CORROSION STUDY OF AMORPHOUS METAL RIBBONS

    SciTech Connect

    Lian, T; Day, S D; Farmer, J C

    2006-07-31

    Corrosion costs the Department of Defense billions of dollars every year, with an immense quantity of material in various structures undergoing corrosion. For example, in addition to fluid and seawater piping, ballast tanks, and propulsions systems, approximately 345 million square feet of structure aboard naval ships and crafts require costly corrosion control measures. The use of advanced corrosion-resistant materials to prevent the continuous degradation of this massive surface area would be extremely beneficial. The potential advantages of amorphous metals have been recognized for some time [Latanison 1985]. Iron-based corrosion-resistant, amorphous-metal coatings under development may prove important for maritime applications [Farmer et al. 2005]. Such materials could also be used to coat the entire outer surface of containers for the transportation and long-term storage of spent nuclear fuel, or to protect welds and heat affected zones, thereby preventing exposure to environments that might cause stress corrosion cracking [Farmer et al. 1991, 2000a, 2000b]. In the future, it may be possible to substitute such high-performance iron-based materials for more-expensive nickel-based alloys, thereby enabling cost savings in a wide variety of industrial applications. It should be noted that thermal-spray ceramic coatings have also been investigated for such applications [Haslam et al. 2005]. This report focuses on the corrosion resistance of iron-based melt-spun amorphous metal ribbons. Melt-Spun ribbon is made by rapid solidification--a stream of molten metal is dropped onto a spinning copper wheel, a process that enables the manufacture of amorphous metals which are unable to be manufactured by conventional cold or hot rolling techniques. The study of melt-spun ribbon allows quick evaluation of amorphous metals corrosion resistance. The melt-spun ribbons included in this study are DAR40, SAM7, and SAM8, SAM1X series, and SAM2X series. The SAM1X series ribbons have

  7. Quantifying Nanoscale Order in Amorphous Materials via Fluctuation Electron Microscopy

    ERIC Educational Resources Information Center

    Bogle, Stephanie Nicole

    2009-01-01

    Fluctuation electron microscopy (FEM) has been used to study the nanoscale order in various amorphous materials. The method is explicitly sensitive to 3- and 4-body atomic correlation functions in amorphous materials; this is sufficient to establish the existence of structural order on the nanoscale, even when the radial distribution function…

  8. LOW-TEMPERATURE CRYSTALLIZATION OF AMORPHOUS SILICATE IN ASTROPHYSICAL ENVIRONMENTS

    SciTech Connect

    Tanaka, Kyoko K.; Yamamoto, Tetsuo; Kimura, Hiroshi

    2010-07-01

    We construct a theoretical model for low-temperature crystallization of amorphous silicate grains induced by exothermic chemical reactions. As a first step, the model is applied to the annealing experiments, in which the samples are (1) amorphous silicate grains and (2) amorphous silicate grains covered with an amorphous carbon layer. We derive the activation energies of crystallization for amorphous silicate and amorphous carbon from the analysis of the experiments. Furthermore, we apply the model to the experiment of low-temperature crystallization of an amorphous silicate core covered with an amorphous carbon layer containing reactive molecules. We clarify the conditions of low-temperature crystallization due to exothermic chemical reactions. Next, we formulate the crystallization conditions so as to be applicable to astrophysical environments. We show that the present crystallization mechanism is characterized by two quantities: the stored energy density Q in a grain and the duration of the chemical reactions {tau}. The crystallization conditions are given by Q>Q{sub min} and {tau} < {tau}{sub cool} regardless of details of the reactions and grain structure, where {tau}{sub cool} is the cooling timescale of the grains heated by exothermic reactions, and Q{sub min} is minimum stored energy density determined by the activation energy of crystallization. Our results suggest that silicate crystallization occurs in wider astrophysical conditions than hitherto considered.

  9. Polarization effects in femtosecond laser induced amorphization of monocrystalline silicon

    NASA Astrophysics Data System (ADS)

    Bai, Feng; Li, Hong-Jin; Huang, Yuan-Yuan; Fan, Wen-Zhong; Pan, Huai-Hai; Wang, Zhuo; Wang, Cheng-Wei; Qian, Jing; Li, Yang-Bo; Zhao, Quan-Zhong

    2016-10-01

    We have used femtosecond laser pulses to ablate monocrystalline silicon wafer. Raman spectroscopy and X-ray diffraction analysis of ablation surface indicates horizontally polarized laser beam shows an enhancement in amorphization efficiency by a factor of 1.6-1.7 over the circularly polarized laser ablation. This demonstrates that one can tune the amorphization efficiency through the polarization of irradiation laser.

  10. Electrically conducting ternary amorphous fully oxidized materials and their application

    NASA Technical Reports Server (NTRS)

    Giauque, Pierre (Inventor); Nicolet, Marc (Inventor); Gasser, Stefan M. (Inventor); Kolawa, Elzbieta A. (Inventor); Cherry, Hillary (Inventor)

    2004-01-01

    Electrically active devices are formed using a special conducting material of the form Tm--Ox mixed with SiO2 where the materials are immiscible. The immiscible materials are forced together by using high energy process to form an amorphous phase of the two materials. The amorphous combination of the two materials is electrically conducting but forms an effective barrier.

  11. Pressure-induced transformations in amorphous silicon: A computational study

    SciTech Connect

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

    2014-02-14

    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.

  12. Method for improving the stability of amorphous silicon

    DOEpatents

    Branz, Howard M.

    2004-03-30

    A method of producing a metastable degradation resistant amorphous hydrogenated silicon film is provided, which comprises the steps of growing a hydrogenated amorphous silicon film, the film having an exposed surface, illuminating the surface using an essentially blue or ultraviolet light to form high densities of a light induced defect near the surface, and etching the surface to remove the defect.

  13. Using Amorphous Phases in the Design of Structural Alloys

    NASA Astrophysics Data System (ADS)

    Schwarz, R. B.; Nash, P.

    1989-01-01

    The recent discovery that amorphous alloy powders can be prepared by mechanically alloying a mixture of pure crystalline intermetallics is opening new windows to the synthesis of engineering materials. Amorphous powders synthesized by mechanical alloying may find application in the design of structural alloys, high thermal conductivity alloys, and metal-matrix composites.

  14. Superlattice doped layers for amorphous silicon photovoltaic cells

    DOEpatents

    Arya, Rajeewa R.

    1988-01-12

    Superlattice doped layers for amorphous silicon photovoltaic cells comprise a plurality of first and second lattices of amorphous silicon alternatingly formed on one another. Each of the first lattices has a first optical bandgap and each of the second lattices has a second optical bandgap different from the first optical bandgap. A method of fabricating the superlattice doped layers also is disclosed.

  15. Amorphization and nanocrystallization of silcon under shock compression

    DOE PAGES

    Remington, B. A.; Wehrenberg, C. E.; Zhao, S.; Hahn, E. N.; Kad, B.; Bringa, E. M.; Meyers, M. A.

    2015-11-06

    High-power, short-duration, laser-driven, shock compression and recovery experiments on [001] silicon unveiled remarkable structural changes above a pressure threshold. Two distinct amorphous regions were identified: (a) a bulk amorphous layer close to the surface and (b) amorphous bands initially aligned with {111} slip planes. Further increase of the laser energy leads to the re-crystallization of amorphous silicon into nanocrystals with high concentration of nano-twins. This amorphization is produced by the combined effect of high magnitude hydrostatic and shear stresses under dynamic shock compression. Shock-induced defects play a very important role in the onset of amorphization. Calculations of the free energymore » changes with pressure and shear, using the Patel-Cohen methodology, are in agreement with the experimental results. Molecular dynamics simulation corroborates the amorphization, showing that it is initiated by the nucleation and propagation of partial dislocations. As a result, the nucleation of amorphization is analyzed qualitatively by classical nucleation theory.« less

  16. Fabrication and Characterization of Amorphous/Nanocrystalline Thin Film Composite

    NASA Astrophysics Data System (ADS)

    Newton, Benjamin S.

    Combining the absorption abilities of amorphous silicon and the electron transport capabilities of crystalline silicon would be a great advantage to not only solar cells but other semiconductor devices. In this work composite films were created using molecular beam epitaxy and electron beam deposition interchangeably as a method to create metallic precursors. Aluminum induced crystallization techniques were used to convert an amorphous silicon film with a capping layer of aluminum nanodots into a film composed of a mixture of amorphous silicon and nanocrystalline silicon. This layer was grown into the amorphous layer by cannibalizing a portion of the amorphous silicon material during the aluminum induced crystallization. Characterization was performed on films and metallic precursors utilizing SEM, TEM, ellipsometry and spectrophotometer.

  17. 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.

  18. Parametrized dielectric functions of amorphous GeSn alloys

    NASA Astrophysics Data System (ADS)

    D'Costa, Vijay Richard; Wang, Wei; Schmidt, Daniel; Yeo, Yee-Chia

    2015-09-01

    We obtained the complex dielectric function of amorphous Ge1-xSnx (0 ≤ x ≤ 0.07) alloys using spectroscopic ellipsometry from 0.4 to 4.5 eV. Amorphous GeSn films were formed by room-temperature implantation of phosphorus into crystalline GeSn alloys grown by molecular beam epitaxy. The optical response of amorphous GeSn alloys is similar to amorphous Ge and can be parametrized using a Kramers-Kronig consistent Cody-Lorentz dispersion model. The parametric model was extended to account for the dielectric functions of amorphous Ge0.75Sn0.25 and Ge0.50Sn0.50 alloys from literature. The compositional dependence of band gap energy Eg and parameters associated with the Lorentzian oscillator have been determined. The behavior of these parameters with varying x can be understood in terms of the alloying effect of Sn on Ge.

  19. Atomistic simulation of damage accumulation and amorphization in Ge

    SciTech Connect

    Gomez-Selles, Jose L. Martin-Bragado, Ignacio; Claverie, Alain; Benistant, Francis

    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. 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.

  20. Atomic structure of amorphous shear bands in boron carbide.

    PubMed

    Reddy, K Madhav; Liu, P; Hirata, A; Fujita, T; Chen, M W

    2013-01-01

    Amorphous shear bands are the main deformation and failure mode of super-hard boron carbide subjected to shock loading and high pressures at room temperature. Nevertheless, the formation mechanisms of the amorphous shear bands remain a long-standing scientific curiosity mainly because of the lack of experimental structure information of the disordered shear bands, comprising light elements of carbon and boron only. Here we report the atomic structure of the amorphous shear bands in boron carbide characterized by state-of-the-art aberration-corrected transmission electron microscopy. Distorted icosahedra, displaced from the crystalline matrix, were observed in nano-sized amorphous bands that produce dislocation-like local shear strains. These experimental results provide direct experimental evidence that the formation of amorphous shear bands in boron carbide results from the disassembly of the icosahedra, driven by shear stresses.

  1. Moringa coagulant as a stabilizer for amorphous solids: Part I.

    PubMed

    Bhende, Santosh; Jadhav, Namdeo

    2012-06-01

    Stabilization of amorphous state is a focal area for formulators to reap benefits related with solubility and consequently bioavailability of poorly soluble drugs. In the present work, an attempt has been made to explore the potential of moringa coagulant as an amorphous state stabilizer by investigating its role in stabilization of spray-dried (amorphous) ibuprofen, meloxicam and felodipine. Thermal studies like glass forming ability, glass transition temperature, hot stage microscopy and DSC were carried out for understanding thermodynamic stabilization of drugs. PXRD and dissolution studies were performed to support contribution of moringa coagulant. Studies showed that hydrogen bonding and electrostatic interactions between drug and moringa coagulant are responsible for amorphous state stabilization as explored by ATR-FTIR and molecular docking. Especially, H-bonding was found to be predominant mechanism for drug stabilization. Therein, arginine (basic amino acid in coagulant) exhibited various interactions and played important role in stabilization of aforesaid amorphous drugs. PMID:22359158

  2. Salt Fog Testing Iron-Based Amorphous Alloys

    SciTech Connect

    Rebak, Raul B.; Aprigliano, Louis F.; Day, S. Daniel; Farmer, Joseph C.

    2007-07-01

    Iron-based amorphous alloys are hard and highly corrosion resistant, which make them desirable for salt water and other applications. These alloys can be produced as powder and can be deposited as coatings on any surface that needs to be protected from the environment. It was of interest to examine the behavior of these amorphous alloys in the standard salt-fog testing ASTM B 117. Three different amorphous coating compositions were deposited on 316L SS coupons and exposed for many cycles of the salt fog test. Other common engineering alloys such as 1018 carbon steel, 316L SS and Hastelloy C-22 were also tested together with the amorphous coatings. Results show that amorphous coatings are resistant to rusting in salt fog. Partial devitrification may be responsible for isolated rust spots in one of the coatings. (authors)

  3. Amorphous molybdenum sulfides as hydrogen evolution catalysts.

    PubMed

    Morales-Guio, Carlos G; Hu, Xile

    2014-08-19

    Providing energy for a population projected to reach 9 billion people within the middle of this century is one of the most pressing societal issues. Burning fossil fuels at a rate and scale that satisfy our near-term demand will irreversibly damage the living environment. Among the various sources of alternative and CO2-emission-free energies, the sun is the only source that is capable of providing enough energy for the whole world. Sunlight energy, however, is intermittent and requires an efficient storage mechanism. Sunlight-driven water splitting to make hydrogen is widely considered as one of the most attractive methods for solar energy storage. Water splitting needs a hydrogen evolution catalyst to accelerate the rate of hydrogen production and to lower the energy loss in this process. Precious metals such as Pt are superior catalysts, but they are too expensive and scarce for large-scale applications. In this Account, we summarize our recent research on the preparation, characterization, and application of amorphous molybdenum sulfide catalysts for the hydrogen evolution reaction. The catalysts can be synthesized by electrochemical deposition under ambient conditions from readily available and inexpensive precursors. The catalytic activity is among the highest for nonprecious catalysts. For example, at a loading of 0.2 mg/cm(2), the optimal catalyst delivers a current density of 10 mA/cm(2) at an overpotential of 160 mV. The growth mechanism of the electrochemically deposited film catalysts was revealed by an electrochemical quartz microcrystal balance study. While different electrochemical deposition methods produce films with different initial compositions, the active catalysts are the same and are identified as a "MoS(2+x)" species. The activity of the film catalysts can be further promoted by divalent Fe, Co, and Ni ions, and the origins of the promotional effects have been probed. Highly active amorphous molybdenum sulfide particles can also be prepared

  4. Characteristics of amorphous kerogens fractionated from terrigenous sedimentary rocks

    NASA Astrophysics Data System (ADS)

    Suzuki, Noriyuki

    1984-02-01

    A preliminary attempt to fractionate amorphous kerogens from terrigenous bulk kerogen by a benzene-water two phase partition method under acidic condition was made. Microscopic observation revealed that amorphous kerogens and structured kerogens were fractionated effectively by this method. Characteristics of the amorphous and structured kerogens fractionated by this method were examined by some chemical analyses and compared with those of the bulk kerogen and humic acid isolated from the same rock sample (Haizume Formation, Pleistocene, Japan). The elemental and infrared (IR) analyses showed that the amorphous kerogen fraction had the highest atomic H/C ratio and the lowest atomic N/C ratio and was the richest in aliphatic structures and carbonyl and carboxyl functional groups. Quantities of fatty acids from the saponification products of each geopolymer were in agreement with the results of elemental and IR analyses. Distribution of the fatty acids was suggestive that more animal lipids participate in the formation of amorphous kerogens because of the abundance of relatively lower molecular weight fatty acids (such as C 16 and C 18 acids) in saponification products of amorphous kerogens. On the other hand, although the amorphous kerogen fraction tends to be rich in aliphatic structures compared with bulk kerogen of the same rock samples, van Krevelen plots of elemental compositions of kerogens from the core samples (Nishiyama Oil Field, Tertiary, Japan) reveal that the amorphous kerogen fraction is not necessarily characterized by markedly high atomic H/C ratio. This was attributed to the oxic environment of deposition and the abundance of biodegraded terrestrial amorphous organic matter in the amorphous kerogen fraction used in this work.

  5. High-Density Amorphous Ice, the Frost on Interstellar Grains

    NASA Technical Reports Server (NTRS)

    Jenniskens, P.; Blake, D. F.; Wilson, M. A.; Pohorille, A.

    1995-01-01

    Most water ice in the universe is in a form which does not occur naturally on Earth and of which only minimal amounts have been made in the laboratory. We have encountered this 'high-density amorphous ice' in electron diffraction experiments of low-temperature (T less than 30 K) vapor-deposited water and have subsequently modeled its structure using molecular dynamics simulations. The characteristic feature of high-density amorphous ice is the presence of 'interstitial' oxygen pair distances between 3 and 4 A. However, we find that the structure is best described as a collapsed lattice of the more familiar low-density amorphous form. These distortions are frozen in at temperatures below 38 K because, we propose, it requires the breaking of one hydrogen bond, on average, per molecule to relieve the strain and to restructure the lattice to that of low-density amorphous ice. Several features of astrophysical ice analogs studied in laboratory experiments are readily explained by the structural transition from high-density amorphous ice into low-density amorphous ice. Changes in the shape of the 3.07 gm water band, trapping efficiency of CO, CO loss, changes in the CO band structure, and the recombination of radicals induced by low-temperature UV photolysis all covary with structural changes that occur in the ice during this amorphous to amorphous transition. While the 3.07 micrometers ice band in various astronomical environments can be modeled with spectra of simple mixtures of amorphous and crystalline forms, the contribution of the high-density amorphous form nearly always dominates.

  6. Theoretical studies of amorphous silicon and hydrogenated amorphous silicon with molecular dynamics simulations

    SciTech Connect

    Kwon, I.

    1991-12-20

    Amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) have been studied with molecular dynamics simulations. The structural, vibrational, and electronic properties of these materials have been studied with computer-generated structural models and compare well with experimental observations. The stability of a-si and a-Si:H have been studied with the aim of understanding microscopic mechanisms underlying light-induced degradation in a-Si:H (the Staebler-Wronski effect). With a view to understanding thin film growth processes, a-Si films have been generated with molecular dynamics simulations by simulating the deposition of Si-clusters on a Si(111) substrate. A new two- and three-body interatomic potential for Si-H interactions has been developed. The structural properties of a-Si:H networks are in good agreement with experimental measurements. The presence of H atoms reduces strain and disorder relative to networks without H.

  7. Nanostructural characterization of amorphous diamondlike carbon films

    SciTech Connect

    SIEGAL,MICHAEL P.; TALLANT,DAVID R.; MARTINEZ-MIRANDA,L.J.; BARBOUR,J. CHARLES; SIMPSON,REGINA L.; OVERMYER,DONALD L.

    2000-01-27

    Nanostructural characterization of amorphous diamondlike carbon (a-C) films grown on silicon using pulsed-laser deposition (PLD) is correlated to both growth energetic and film thickness. Raman spectroscopy and x-ray reflectivity probe both the topological nature of 3- and 4-fold coordinated carbon atom bonding and the topographical clustering of their distributions within a given film. In general, increasing the energetic of PLD growth results in films becoming more ``diamondlike'', i.e. increasing mass density and decreasing optical absorbance. However, these same properties decrease appreciably with thickness. The topology of carbon atom bonding is different for material near the substrate interface compared to material within the bulk portion of an a-C film. A simple model balancing the energy of residual stress and the free energies of resulting carbon topologies is proposed to provide an explanation of the evolution of topographical bonding clusters in a growing a-C film.

  8. Amorphous silicon-based microchannel plates

    NASA Astrophysics Data System (ADS)

    Franco, Andrea; Riesen, Yannick; Wyrsch, Nicolas; Dunand, Sylvain; Powolny, François; Jarron, Pierre; Ballif, Christophe

    2012-12-01

    Microchannel plates (MCP) based on hydrogenated amorphous silicon (a-Si:H) were recently introduced to overcome some of the limitations of crystalline silicon and glass MCP. The typical thickness of a-Si:H based MCPs (AMCP) ranges between 80 and 100 μm and the micromachining of the channels is realized by deep reactive ion etching (DRIE). Advantages and issues regarding the fabrication process are presented and discussed. Electron amplification is demonstrated and analyzed using Electron Beam Induced Current (EBIC) technique. The gain increases as a function of the bias voltage, limited to -340 V on account of high leakage currents across the structure. EBIC maps on 10° tilted samples confirm that the device active area extend to the entire channel opening. AMCP characterization with the electron beam shows gain saturation and signal quenching which depends on the effectiveness of the charge replenishment in the channel walls.

  9. Bulk amorphous steels based on Fe alloys

    DOEpatents

    Lu, ZhaoPing; Liu, Chain T.

    2006-05-30

    A bulk amorphous alloy has the approximate composition: Fe.sub.(100-a-b-c-d-e)Y.sub.aMn.sub.bT.sub.cM.sub.dX.sub.e wherein: T includes at least one of the group consisting of: Ni, Cu, Cr and Co; M includes at least one of the group consisting of W, Mo, Nb, Ta, Al and Ti; X includes at least one of the group consisting of Co, Ni and Cr; a is an atomic percentage, and a<5; b is an atomic percentage, and b.ltoreq.25; c is an atomic percentage, and c.ltoreq.25; d is an atomic percentage, and d.ltoreq.25; and e is an atomic percentage, and 5.ltoreq.e.ltoreq.30.

  10. Orientational fluctuations of amorphous nematogenic solids

    NASA Astrophysics Data System (ADS)

    Ye, Fangfu; Lu, Bing; Goldbart, Paul

    2012-02-01

    Amorphous nematogenic solids (ANS) are media comprising rod-like nematogens that have been randomly linked to form elastically deformable macroscopic networks. Classes of ANS include chemical nematogen gels (i.e., networks of small molecules) and liquid crystalline elastomers (built from crosslinked nematogen-containing macromolecules), as well as biophysical networks such as those composed of actin filaments. We use a method inspired by the cavity approach to construct a replica free energy for these random systems, and investigate the correlations of the thermal fluctuations of the orientational alignment of the nematogens at spatially separated points. We identify two qualitatively distinct regimes: (a) a weakly localized regime, in which the correlations decay exponentially with separation; and (b) a strongly localized regime, characterized by correlations that also decay but oscillate as they do.

  11. Ultrafast recombination and trapping in amorphous silicon

    NASA Astrophysics Data System (ADS)

    Esser, A.; Seibert, K.; Kurz, H.; Parsons, G. N.; Wang, C.; Davidson, B. N.; Lucovsky, G.; Nemanich, R. J.

    1990-02-01

    We have studied the time-resolved reflectivity and transmission changes induced by femtosecond laser pulses in hydrogenated and nonhydrogenated amorphous silicon thin films, a-Si:H and a-Si, respectively. By varying the pump power, and hence the photoexcited free-carrier densities, by several orders of magnitude, a quadratic, nonradiative recombination process has been identified that controls the density of free carriers on a picosecond time scale for excitation levels above 5×1018 cm-3 in a-Si:H and above 5×1019 cm-3 in a-Si. At lower free-carrier densities, the reflectivity transients display the dynamics expected from a trapping mechanism. We suggest that the process that dominates for the higher free-carrier densities may result from Auger recombination but with a dependence on the carrier density that is different from that which has been observed in crystalline semiconductors where k selection prevails.

  12. Polarization Stability of Amorphous Piezoelectric Polyimides

    NASA Technical Reports Server (NTRS)

    Park, C.; Ounaies, Z.; Su, J.; Smith, J. G., Jr.; Harrison, J. S.

    2000-01-01

    Amorphous polyimides containing polar functional groups have been synthesized and investigated for potential use as high temperature piezoelectric sensors. The thermal stability of the piezoelectric effect of one polyimide was evaluated as a function of various curing and poling conditions under dynamic and static thermal stimuli. First, the polymer samples were thermally cycled under strain by systematically increasing the maximum temperature from 50 C to 200 C while the piezoelectric strain coefficient was being measured. Second, the samples were isothermally aged at an elevated temperature in air, and the isothermal decay of the remanent polarization was measured at room temperature as a function of time. Both conventional and corona poling methods were evaluated. This material exhibited good thermal stability of the piezoelectric properties up to 100 C.

  13. Breakdown of continuum elasticity in amorphous solids

    NASA Astrophysics Data System (ADS)

    Lerner, Edan; DeGiuli, Eric; Düring, Gustavo; Wyart, Matthieu

    We show numerically that the response of simple amorphous solids (elastic networks and particle packings) to a local force dipole is characterized by a lengthscale $\\ell_c$ that diverges as unjamming is approached as $\\ell_c \\sim (z - 2d)^{-1/2}$, where $z \\ge 2d$ is the mean coordination, and $d$ is the spatial dimension, at odds with previous numerical claims. We also show how the magnitude of the lengthscale $\\ell_c$ is amplified by the presence of internal stresses in the disordered solid. Our data suggests a divergence of $\\ell_c\\sim (p_c-p)^{-1/4}$ with proximity to a critical internal stress $p_c$ at which soft elastic modes become unstable.

  14. Evidence for Valence Alternation in Amorphous Selenium

    NASA Astrophysics Data System (ADS)

    Xiaodong, Zhang; Drabold, D. A.

    1998-05-01

    A molecular-dynamics simulation has been carried out for amorphous selenium. The simulation used 64 atoms as well as 216 atoms in a constant volume simple cubic cell. The pair correlation function g(r) and structure factors S(Q) were computed and compared with experimental and previous theoretical data. The coordination number is exactly 2 in both 64 atoms and 216 atoms model. In 64 atoms model, only 1 intimate valence alternation pair (IVAP) type defect was produced. The majority defect types are IVAP and valence alternation pair (VAP) in 216 atoms model. The electronic density function of state and the localization of the electronic state also manisfest some characternistic of VAP defect type. The results give a theoretical evidence for valence alternation in a-Se.

  15. Buckling instability in amorphous carbon films

    NASA Astrophysics Data System (ADS)

    Zhu, X. D.; Narumi, K.; Naramoto, H.

    2007-06-01

    In this paper, we report the buckling instability in amorphous carbon films on mirror-polished sapphire (0001) wafers deposited by ion beam assisted deposition at various growth temperatures. For the films deposited at 150 °C, many interesting stress relief patterns are found, which include networks, blisters, sinusoidal patterns with π-shape, and highly ordered sinusoidal waves on a large scale. Starting at irregular buckling in the centre, the latter propagate towards the outer buckling region. The maximum length of these ordered patterns reaches 396 µm with a height of ~500 nm and a wavelength of ~8.2 µm. However, the length decreases dramatically to 70 µm as the deposition temperature is increased to 550 °C. The delamination of the film appears instead of sinusoidal waves with a further increase of the deposition temperature. This experimental observation is correlated with the theoretic work of Crosby (1999 Phys. Rev. E 59 R2542).

  16. Amorphous materials molded IR lens progress report

    NASA Astrophysics Data System (ADS)

    Hilton, A. R., Sr.; McCord, James; Timm, Ronald; Le Blanc, R. A.

    2008-04-01

    Amorphous Materials began in 2000 a joint program with Lockheed Martin in Orlando to develop molding technology required to produce infrared lenses from chalcogenide glasses. Preliminary results were reported at this SPIE meeting by Amy Graham1 in 2003. The program ended in 2004. Since that time, AMI has concentrated on improving results from two low softening glasses, Amtir 4&5. Both glasses have been fully characterized and antireflection coatings have been developed for each. Lenses have been molded from both glasses, from Amtir 6 and from C1 Core glass. A Zygo unit is used to evaluate the results of each molded lens as a guide to improving the molding process. Expansion into a larger building has provided room for five production molding units. Molded lens sizes have ranged from 8 mm to 136 mm in diameter. Recent results will be presented

  17. Short range atomic migration in amorphous silicon

    NASA Astrophysics Data System (ADS)

    Strauß, F.; Jerliu, B.; Geue, T.; Stahn, J.; Schmidt, H.

    2016-05-01

    Experiments on self-diffusion in amorphous silicon between 400 and 500 °C are presented, which were carried out by neutron reflectometry in combination with 29Si/natSi isotope multilayers. Short range diffusion is detected on a length scale of about 2 nm, while long range diffusion is absent. Diffusivities are in the order of 10-19-10-20 m2/s and decrease with increasing annealing time, reaching an undetectable low value for long annealing times. This behavior is strongly correlated to structural relaxation and can be explained as a result of point defect annihilation. Diffusivities for short annealing times of 60 s follow the Arrhenius law with an activation enthalpy of (0.74 ± 0.21) eV, which is interpreted as the activation enthalpy of Si migration.

  18. Enthalpy of formation of amorphous silica

    SciTech Connect

    Klyuchnikov, V.A.; Voronkov, M.G.; Landa, L.M.; Pepekin, V.I.; Tikhenko, T.M.; Shvets, G.N.; Popov, V.T.

    1987-07-01

    In calculating the formation heat of organosilicon compounds from the results of their combustion heat on oxygen it is necessary to have a reliable value of the standard formation heat of hydrated silica. This paper, in trying to assess this property, examines the following factors: the character of the surface, the structure and specific concentration of surface silicon hydroxide groups, and the energy of its wetting with water. Combustion experiments are carried out and described. It is concluded that the formation heat of amorphous silica is not a constant value and is determined by the character of its surface and degree of hydration. For this reason, in the combustion of organosilicon compounds, the formation heat of silica should be determined experimentally.

  19. Lithium transport through nanosized amorphous silicon layers.

    PubMed

    Hüger, Erwin; Dörrer, Lars; Rahn, Johanna; Panzner, Tobias; Stahn, Jochen; Lilienkamp, Gerhard; Schmidt, Harald

    2013-03-13

    Lithium migration in nanostructured electrode materials is important for an understanding and improvement of high energy density lithium batteries. An approach to measure lithium transport through nanometer thin layers of relevant electrochemical materials is presented using amorphous silicon as a model system. A multilayer consisting of a repetition of five [(6)LiNbO3(15 nm)/Si (10 nm)/(nat)LiNbO3 (15 nm)/Si (10 nm)] units is used for analysis, where LiNbO3 is a Li tracer reservoir. It is shown that the change of the relative (6)Li/(7)Li isotope fraction in the LiNbO3 layers by lithium diffusion through the nanosized silicon layers can be monitored nondestructively by neutron reflectometry. The results can be used to calculate transport parameters.

  20. Structural relaxation of vacancies in amorphous silicon

    SciTech Connect

    Kim, E.; Lee, Y.H.; Chen, C.; Pang, T.

    1997-07-01

    The authors have studied the structural relaxation of vacancies in amorphous silicon (a-Si) using a tight-binding molecular-dynamics method. The most significant difference between vacancies in a-Si and those in crystalline silicon (c-Si) is that the deep gap states do not show up in a-Si. This difference is explained through the unusual behavior of the structural relaxation near the vacancies in a-Si, which enhances the sp{sup 2} + p bonding near the band edges. They have also observed that the vacancies do not migrate below 450 K although some of them can still be annihilated, particularly at high defect density due to large structural relaxation.

  1. How does an amorphous surface influence molecular binding?--ovocleidin-17 and amorphous calcium carbonate.

    PubMed

    Freeman, Colin L; Harding, John H; Quigley, David; Rodger, P Mark

    2015-07-14

    Atomistic molecular dynamics simulations of dehydrated amorphous calcium carbonate interacting with the protein ovocleidin-17 are presented. These simulations demonstrate that the amorphisation of the calcium carbonate surface removes water structure from the surface. This reduction of structure allows the protein to bind with many residues, unlike on crystalline surfaces where binding is strongest when only a few residues are attached to the surface. Basic residues are observed to dominate the binding interactions. The implications for protein control over crystallisation are discussed.

  2. Castable Amorphous Metal Mirrors and Mirror Assemblies

    NASA Technical Reports Server (NTRS)

    Hofmann, Douglas C.; Davis, Gregory L.; Agnes, Gregory S.; Shapiro, Andrew A.

    2013-01-01

    A revolutionary way to produce a mirror and mirror assembly is to cast the entire part at once from a metal alloy that combines all of the desired features into the final part: optical smoothness, curvature, flexures, tabs, isogrids, low CTE, and toughness. In this work, it has been demonstrated that castable mirrors are possible using bulk metallic glasses (BMGs, also called amorphous metals) and BMG matrix composites (BMGMCs). These novel alloys have all of the desired mechanical and thermal properties to fabricate an entire mirror assembly without machining, bonding, brazing, welding, or epoxy. BMGs are multi-component metal alloys that have been cooled in such a manner as to avoid crystallization leading to an amorphous (non-crystalline) microstructure. This lack of crystal structure and the fact that these alloys are glasses, leads to a wide assortment of mechanical and thermal properties that are unlike those observed in crystalline metals. Among these are high yield strength, carbide-like hardness, low melting temperatures (making them castable like aluminum), a thermoplastic processing region (for improving smoothness), low stiffness, high strength-to-weight ratios, relatively low CTE, density similar to titanium alloys, high elasticity and ultra-smooth cast parts (as low as 0.2-nm surface roughness has been demonstrated in cast BMGs). BMGMCs are composite alloys that consist of a BMG matrix with crystalline dendrites embedded throughout. BMGMCs are used to overcome the typically brittle failure observed in monolithic BMGs by adding a soft phase that arrests the formation of cracks in the BMG matrix. In some cases, BMGMCs offer superior castability, toughness, and fatigue resistance, if not as good a surface finish as BMGs. This work has demonstrated that BMGs and BMGMCs can be cast into prototype mirrors and mirror assemblies without difficulty.

  3. Anomalous hopping conduction in nanocrystalline/amorphous composites and amorphous semiconductor thin films

    NASA Astrophysics Data System (ADS)

    Kakalios, James; Bodurtha, Kent

    Composite nanostructured materials consisting of nanocrystals (nc) embedded within a thin film amorphous matrix can exhibit novel opto-electronic properties. Composite films are synthesized in a dual-chamber co-deposition PECVD system capable of producing nanocrystals of material A and embedding then within a thin film matrix of material B. Electronic conduction in composite thin films of hydrogenated amorphous silicon (a-Si:H) containing nc-germanium or nc-silicon inclusions, as well as in undoped a-Si:H, does not follow an Arrhenius temperature dependence, but rather is better described by an anomalous hopping expression (exp[-(To/T)3/4) , as determined from the ``reduced activation energy'' proposed by Zabrodskii and Shlimak. This temperature dependence has been observed in other thin film resistive materials, such as ultra-thin disordered films of Ag, Bi, Pb and Pd; carbon-black polymer composites; and weakly coupled Au and ZnO quantum dot arrays. There is presently no accepted theoretical understanding of this expression. The concept of a mobility edge, accepted for over four decades, appears to not be necessary to account for charge transport in amorphous semiconductors. Supported by NSF-DMR and the Minnesota Nano Center.

  4. Amorphous Calcium Carbonate Based-Microparticles for Peptide Pulmonary Delivery.

    PubMed

    Tewes, Frederic; Gobbo, Oliviero L; Ehrhardt, Carsten; Healy, Anne Marie

    2016-01-20

    Amorphous calcium carbonate (ACC) is known to interact with proteins, for example, in biogenic ACC, to form stable amorphous phases. The control of amorphous/crystalline and inorganic/organic ratios in inhalable calcium carbonate microparticles may enable particle properties to be adapted to suit the requirements of dry powders for pulmonary delivery by oral inhalation. For example, an amorphous phase can immobilize and stabilize polypeptides in their native structure and amorphous and crystalline phases have different mechanical properties. Therefore, inhalable composite microparticles made of inorganic (i.e., calcium carbonate and calcium formate) and organic (i.e., hyaluronan (HA)) amorphous and crystalline phases were investigated for peptide and protein pulmonary aerosol delivery. The crystalline/amorphous ratio and polymorphic form of the inorganic component was altered by changing the microparticle drying rate and by changing the ammonium carbonate and HA initial concentration. The bioactivity of the model peptide, salmon calcitonin (sCT), coprocessed with alpha-1-antitrypsin (AAT), a model protein with peptidase inhibitor activity, was maintained during processing and the microparticles had excellent aerodynamic properties, making them suitable for pulmonary aerosol delivery. The bioavailability of sCT after aerosol delivery as sCT and AAT-loaded composite microparticles to rats was 4-times higher than that of sCT solution.

  5. Amorphous Calcium Carbonate Based-Microparticles for Peptide Pulmonary Delivery.

    PubMed

    Tewes, Frederic; Gobbo, Oliviero L; Ehrhardt, Carsten; Healy, Anne Marie

    2016-01-20

    Amorphous calcium carbonate (ACC) is known to interact with proteins, for example, in biogenic ACC, to form stable amorphous phases. The control of amorphous/crystalline and inorganic/organic ratios in inhalable calcium carbonate microparticles may enable particle properties to be adapted to suit the requirements of dry powders for pulmonary delivery by oral inhalation. For example, an amorphous phase can immobilize and stabilize polypeptides in their native structure and amorphous and crystalline phases have different mechanical properties. Therefore, inhalable composite microparticles made of inorganic (i.e., calcium carbonate and calcium formate) and organic (i.e., hyaluronan (HA)) amorphous and crystalline phases were investigated for peptide and protein pulmonary aerosol delivery. The crystalline/amorphous ratio and polymorphic form of the inorganic component was altered by changing the microparticle drying rate and by changing the ammonium carbonate and HA initial concentration. The bioactivity of the model peptide, salmon calcitonin (sCT), coprocessed with alpha-1-antitrypsin (AAT), a model protein with peptidase inhibitor activity, was maintained during processing and the microparticles had excellent aerodynamic properties, making them suitable for pulmonary aerosol delivery. The bioavailability of sCT after aerosol delivery as sCT and AAT-loaded composite microparticles to rats was 4-times higher than that of sCT solution. PMID:26692360

  6. Rate of H2 formation on amorphous grains

    NASA Technical Reports Server (NTRS)

    Smoluchowski, R.

    1981-01-01

    The rate of formation of molecular hydrogen from hydrogen atoms adsorbed on amorphous grains taken to represent interstellar dust grains is analyzed. Following a brief review of the structure and thermodynamics of amorphous grains and the evidence that interstellar grains are indeed amorphous, consideration is given to the mechanism of formation of H2 molecules by the impact of H atoms on grains with adsorbed H atoms, and it is concluded that on amorphous grains, molecule formation will only occur if H atoms are adsorbed within a distance on the order of 10 A of each other. Rates of H2 formation on single crystal and polycrystalline grains are then calculated and compared with those for amorphous grains, and it is shown that, except for certain temperatures and high H atom densities, the rates of H2 formation on polycrystalline and amorphous grains are up to a few orders of magnitude lower than on single crystals. The results suggest that amorphous grains will lead to H2 clouds with irregular and sharply delineated features in contrast to the more uniform clouds formed on crystalline grains.

  7. Health hazards due to the inhalation of amorphous silica.

    PubMed

    Merget, R; Bauer, T; Küpper, H U; Philippou, S; Bauer, H D; Breitstadt, R; Bruening, T

    2002-01-01

    Occupational exposure to crystalline silica dust is associated with an increased risk for pulmonary diseases such as silicosis, tuberculosis, chronic bronchitis, chronic obstructive pulmonary disease (COPD) and lung cancer. This review summarizes the current knowledge about the health effects of amorphous (non-crystalline) forms of silica. The major problem in the assessment of health effects of amorphous silica is its contamination with crystalline silica. This applies particularly to well-documented pneumoconiosis among diatomaceous earth workers. Intentionally manufactured synthetic amorphous silicas are without contamination of crystalline silica. These synthetic forms may be classified as (1) wet process silica, (2) pyrogenic ("thermal" or "fumed") silica, and (3) chemically or physically modified silica. According to the different physicochemical properties, the major classes of synthetic amorphous silica are used in a variety of products, e.g. as fillers in the rubber industry, in tyre compounds, as free-flow and anti-caking agents in powder materials, and as liquid carriers, particularly in the manufacture of animal feed and agrochemicals; other uses are found in toothpaste additives, paints, silicon rubber, insulation material, liquid systems in coatings, adhesives, printing inks, plastisol car undercoats, and cosmetics. Animal inhalation studies with intentionally manufactured synthetic amorphous silica showed at least partially reversible inflammation, granuloma formation and emphysema, but no progressive fibrosis of the lungs. Epidemiological studies do not support the hypothesis that amorphous silicas have any relevant potential to induce fibrosis in workers with high occupational exposure to these substances, although one study disclosed four cases with silicosis among subjects exposed to apparently non-contaminated amorphous silica. Since the data have been limited, a risk of chronic bronchitis, COPD or emphysema cannot be excluded. There is no study

  8. Dissolution and analysis of amorphous silica in marine sediments.

    USGS Publications Warehouse

    Eggimann, D.W.; Manheim, F. T.; Betzer, P.R.

    1980-01-01

    The analytical estimation of amorphous silica in selected Atlantic and Antarctic Ocean sediments, the U.S.G.S. standard marine mud (MAG-1), A.A.P.G. clays, and samples from cultures of a marine diatom, Hemidiscus, has been examined. Our values for amorphous silica-rich circum-Antarctic sediments are equal to or greater than literature values, whereas our values for a set of amorphous silica-poor sediments from a transect of the N. Atlantic at 11oN, after appropriate correction for silica released from clays, are significantly lower than previous estimates from the same region. -from Authors

  9. The 'depletion layer' of amorphous p-n junctions

    NASA Technical Reports Server (NTRS)

    Von Roos, O.

    1981-01-01

    It is shown that within reasonable approximations for the density of state distribution within the mobility gap of a:Si, a one-to-one correspondence exists between the electric field distribution in the transition region of an amorphous p-n junction and that in the depletion layer of a crystalline p-n junction. Thus it is inferred that the depletion layer approximation which leads to a parabolic potential distribution within the depletion layer of crystalline junctions also constitutes a fair approximation in the case of amorphous junctions. This fact greatly simplifies an analysis of solid-state electronic devices based on amorphous material (i.e., solar cells).

  10. Amorphous photonic crystals with only short-range order.

    PubMed

    Shi, Lei; Zhang, Yafeng; Dong, Biqin; Zhan, Tianrong; Liu, Xiaohan; Zi, Jian

    2013-10-01

    Distinct from conventional photonic crystals with both short- and long-range order, amorphous photonic crystals that possess only short-range order show interesting optical responses owing to their unique structural features. Amorphous photonic crystals exhibit unique light scattering and transport, which lead to a variety of interesting phenomena such as isotropic photonic bandgaps or pseudogaps, noniridescent structural colors, and light localization. Recent experimental and theoretical advances in the study of amorphous photonic crystals are summarized, focusing on their unique optical properties, artificial fabrication, bionspiration, and potential applications.

  11. Depressurization amorphization of single-crystal boron carbide.

    PubMed

    Yan, X Q; Tang, Z; Zhang, L; Guo, J J; Jin, C Q; Zhang, Y; Goto, T; McCauley, J W; Chen, M W

    2009-02-20

    We report depressurization amorphization of single-crystal boron carbide (B4C) investigated by in situ high-pressure Raman spectroscopy. It was found that localized amorphization of B4C takes place during unloading from high pressures, and nonhydrostatic stresses play a critical role in the high-pressure phase transition. First-principles molecular dynamics simulations reveal that the depressurization amorphization results from pressure-induced irreversible bending of C-B-C atomic chains cross-linking 12 atom icosahedra at the rhombohedral vertices.

  12. An infrared and luminescence study of tritiated amorphous silicon

    SciTech Connect

    Sidhu, L.S.; Kosteski, T.; Kherani, N.P.; Gaspari, F.; Zukotynski, S.; Shmayda, W.

    1997-07-01

    Tritium has been incorporated into amorphous silicon. Infrared spectroscopy shows new infrared vibration modes due to silicon-tritium (Si-T) bonds in the amorphous silicon network. Si-T vibration frequencies are related to Si-H vibration frequencies by simple mass relationships. Inelastic collisions of {beta} particles, produced as a result of tritium decay, with the amorphous silicon network results in the generation of electron-hole pairs. Radiative recombination of these carriers is observed. Dangling bonds associated with the tritium decay reduce luminescence efficiency.

  13. Amorphous Silicates in Primitive Meteoritic Materials: Acfer 094 and IDPs

    NASA Technical Reports Server (NTRS)

    Keller, L. P.; Nakamura-Messenger, K.; Messenger, S.; Walker, Robert M.

    2009-01-01

    The abundance of presolar grains is one measure of the primitive nature of meteoritic materials. Presolar silicates are abundant in meteorites whose matrices are dominated by amorphous silicates such as the unique carbonaceous chondrite Acfer 094. Presolar silicates are even more abundant in chondritic-porous interplanetary dust particles (CP-IDPs). Amorphous silicates in the form of GEMS (glass with embedded metal and sulfides) grains are a major component of CP IDPs. We are studying amorphous silicates in Acfer 094 matrix in order to determine whether they are related to the GEMS grains in CPIDPs

  14. Crystallization of amorphous Fe90Zr10 under ball milling.

    PubMed

    Kwon, Young-Soon; Kim, Ji-Soon; Kim, Jin-Chun; Kwon, Yong-Jae; Povstugar, Ivan; Yelsukov, Eugene; Kim, Cheol-Eeh; Lee, Hyung-Soon

    2010-01-01

    The present study deals with structural transformations induced by high-energy ball-milling of an amorphous Fe90Zr10 alloy prepared by melt-spinning. The amorphous melt-spun ribbons were found to undergo crystallization into BCC alpha-Fe(Zr) nanocrystallites under high-energy ball milling. The decomposition degree of the amorphous phase increased with increasing milling time and intensity. Our results suggest that the observed crystallization is a deformation-induced process rather than a thermally induced one.

  15. Lucky drift impact ionization in amorphous semiconductors

    NASA Astrophysics Data System (ADS)

    Kasap, Safa; Rowlands, J. A.; Baranovskii, S. D.; Tanioka, Kenkichi

    2004-08-01

    The review of avalanche multiplication experiments clearly confirms the existence of the impact ionization effect in this class of semiconductors. The semilogarithmic plot of the impact ionization coefficient (α) versus the reciprocal field (1/F) for holes in a-Se and electrons in a-Se and a-Si :H places the avalanche multiplication phenomena in amorphous semiconductors at much higher fields than those typically reported for crystalline semiconductors with comparable bandgaps. Furthermore, in contrast to well established concepts for crystalline semiconductors, the impact ionization coefficient in a-Se increases with increasing temperature. The McKenzie and Burt [S. McKenzie and M. G. Burt, J. Phys. C 19, 1959 (1986)] version of Ridley's lucky drift (LD) model [B. K. Ridley, J. Phys. C 16, 3373 (1988)] has been applied to impact ionization coefficient versus field data for holes and electrons in a-Se and electrons in a-Si :H. We have extracted the electron impact ionization coefficient versus field (αe vs F) data for a-Si :H from the multiplication versus F and photocurrent versus F data recently reported by M. Akiyama, M. Hanada, H. Takao, K. Sawada, and M. Ishida, Jpn. J. Appl. Phys.41, 2552 (2002). Provided that one accepts the basic assumption of the Ridley LD model that the momentum relaxation rate is faster than the energy relaxation rate, the model can satisfactorily account for impact ionization in amorphous semiconductors even with ionizing excitation across the bandgap, EI=Eg. If λ is the mean free path associated with momentum relaxing collisions and λE is the energy relaxation length associated with energy relaxing collisions, than the LD model requires λE>λ. The application of the LD model with energy and field independent λE to a-Se leads to ionization threshold energies EI that are quite small, less than Eg/2, and requires the possible but improbable ionization of localized states. By making λE=λE(E ,F) energy and field dependent, we were

  16. Application of Laser Design of Amorphous Feco-Based Alloys for the Formation of Amorphous-Crystalline Composites

    NASA Astrophysics Data System (ADS)

    Permyakova, I. E.; Glezer, A. M.; Ivanov, A. A.; Shelyakov, A. V.

    2016-01-01

    Morphological and fractographic features of change of FeCo-based amorphous alloy surfaces after laser treatment are studied in detail. Regimes of laser treatment that allow various degrees of crystallization of the examined alloys to be obtained, including thin (<1 •m) crystal layers on amorphous alloy surfaces, amorphous-crystalline composites, and completely crystalline alloys are adjusted. The Vickers hardness is estimated in zones of selective laser irradiation. The structure of the examined alloys attendant to the change of their mechanical properties is analyzed.

  17. Properties of vaccum arc deposited amorphous hard carbon films

    SciTech Connect

    Anders, S.; Anders, A.; Raoux, S.

    1995-12-31

    Amorphous hard carbon films formed by vacuum arc deposition are, hydrogen-free, dense, and very hard. The properties of amorphous hard carbon films depend strongly on the energy of the incident ions. A technique which is called Plasma Immersion Ion Implantation can be applied to vacuum arc deposition of amorphous hard carbon films to influence the ion energy. We have studied the influence of the ion energy on the elastic modulus determined by an ultrasonic method, and have measured the optical gap for films with the highest sp{sup 3} content we have obtained so far with this deposition technique. The results show an elastic modulus close to that of diamond, and an optical gap of 2.1 eV which is much greater than for amorphous hard carbon films deposited by other techniques.

  18. RF Sputtering for preparing substantially pure amorphous silicon monohydride

    DOEpatents

    Jeffrey, Frank R.; Shanks, Howard R.

    1982-10-12

    A process for controlling the dihydride and monohydride bond densities in hydrogenated amorphous silicon produced by reactive rf sputtering of an amorphous silicon target. There is provided a chamber with an amorphous silicon target and a substrate therein with the substrate and the target positioned such that when rf power is applied to the target the substrate is in contact with the sputtering plasma produced thereby. Hydrogen and argon are fed to the chamber and the pressure is reduced in the chamber to a value sufficient to maintain a sputtering plasma therein, and then rf power is applied to the silicon target to provide a power density in the range of from about 7 watts per square inch to about 22 watts per square inch to sputter an amorphous silicon hydride onto the substrate, the dihydride bond density decreasing with an increase in the rf power density. Substantially pure monohydride films may be produced.

  19. Solid state amorphization kinetic of alpha lactose upon mechanical milling.

    PubMed

    Caron, Vincent; Willart, Jean-François; Lefort, Ronan; Derollez, Patrick; Danède, Florence; Descamps, Marc

    2011-11-29

    It has been previously reported that α-lactose could be totally amorphized by ball milling. In this paper we report a detailed investigation of the structural and microstructural changes by which this solid state amorphization takes place. The investigations have been performed by Powder X-ray Diffraction, Solid State Nuclear Magnetic Resonance ((13)C CP-MAS) and Differential Scanning Calorimetry. The results reveal the structural complexity of the material in the course of its amorphization so that it cannot be considered as a simple mixture made of a decreasing crystalline fraction and an increasing amorphous fraction. Heating this complexity can give rise to a fully nano-crystalline material. The results also show that chemical degradations upon heating are strongly connected to the melting process. PMID:21983262

  20. First principles prediction of amorphous phases using evolutionary algorithms

    NASA Astrophysics Data System (ADS)

    Nahas, Suhas; Gaur, Anshu; Bhowmick, Somnath

    2016-07-01

    We discuss the efficacy of evolutionary method for the purpose of structural analysis of amorphous solids. At present, ab initio molecular dynamics (MD) based melt-quench technique is used and this deterministic approach has proven to be successful to study amorphous materials. We show that a stochastic approach motivated by Darwinian evolution can also be used to simulate amorphous structures. Applying this method, in conjunction with density functional theory based electronic, ionic and cell relaxation, we re-investigate two well known amorphous semiconductors, namely silicon and indium gallium zinc oxide. We find that characteristic structural parameters like average bond length and bond angle are within ˜2% of those reported by ab initio MD calculations and experimental studies.

  1. Predicting Crystallization of Amorphous Drugs with Terahertz Spectroscopy.

    PubMed

    Sibik, Juraj; Löbmann, Korbinian; Rades, Thomas; Zeitler, J Axel

    2015-08-01

    There is a controversy about the extent to which the primary and secondary dielectric relaxations influence the crystallization of amorphous organic compounds below the glass transition temperature. Recent studies also point to the importance of fast molecular dynamics on picosecond-to-nanosecond time scales with respect to the glass stability. In the present study we provide terahertz spectroscopy evidence on the crystallization of amorphous naproxen well below its glass transition temperature and confirm the direct role of Johari-Goldstein (JG) secondary relaxation as a facilitator of the crystallization. We determine the onset temperature Tβ above which the JG relaxation contributes to the fast molecular dynamics and analytically quantify the level of this contribution. We then show there is a strong correlation between the increase in the fast molecular dynamics and onset of crystallization in several chosen amorphous drugs. We believe that this technique has immediate applications to quantify the stability of amorphous drug materials.

  2. First principles prediction of amorphous phases using evolutionary algorithms.

    PubMed

    Nahas, Suhas; Gaur, Anshu; Bhowmick, Somnath

    2016-07-01

    We discuss the efficacy of evolutionary method for the purpose of structural analysis of amorphous solids. At present, ab initio molecular dynamics (MD) based melt-quench technique is used and this deterministic approach has proven to be successful to study amorphous materials. We show that a stochastic approach motivated by Darwinian evolution can also be used to simulate amorphous structures. Applying this method, in conjunction with density functional theory based electronic, ionic and cell relaxation, we re-investigate two well known amorphous semiconductors, namely silicon and indium gallium zinc oxide. We find that characteristic structural parameters like average bond length and bond angle are within ∼2% of those reported by ab initio MD calculations and experimental studies. PMID:27394098

  3. Influence of amorphous structure on polymorphism in vanadia

    NASA Astrophysics Data System (ADS)

    Stone, Kevin H.; Schelhas, Laura T.; Garten, Lauren M.; Shyam, Badri; Mehta, Apurva; Ndione, Paul F.; Ginley, David S.; Toney, Michael F.

    2016-07-01

    Normally we think of the glassy state as a single phase and therefore crystallization from chemically identical amorphous precursors should be identical. Here we show that the local structure of an amorphous precursor is distinct depending on the initial deposition conditions, resulting in significant differences in the final state material. Using grazing incidence total x-ray scattering, we have determined the local structure in amorphous thin films of vanadium oxide grown under different conditions using pulsed laser deposition (PLD). Here we show that the subsequent crystallization of films deposited using different initial PLD conditions result in the formation of different polymorphs of VO2. This suggests the possibility of controlling the formation of metastable polymorphs by tuning the initial amorphous structure to different formation pathways.

  4. Amorphous powders of Al-Hf prepared by mechanical alloying

    SciTech Connect

    Schwarz, R.B.; Hannigan, J.W.; Sheinberg, H.; Tiainen, T.

    1988-01-01

    We synthesized amorphous Al/sub 50/Hf/sub 50/ alloy powder by mechanically alloying an equimolar mixture of crystalline powders of Al and Hf using hexane as a dispersant. We characterized the powder as a function of mechanical-alloying time by scanning electron microscopy, x-ray diffraction, and differential scanning calorimetry. Amorphous Al/sub 50/Hf/sub 50/ powder heated at 10 K s/sup /minus/1/ crystallizes polymorphously at 1003 K into orthorhombic AlHf (CrB-type structure). During mechanical alloying, some hexane decomposes and hydrogen and carbon are incorporated into the amorphous alloy powder. The hydrogen can be removed by annealing the powder by hot pressing at a temperature approximately 30 K below the crystallization temperature. The amorphous compacts have a diamond pyramidal hardness of 1025 DPH. 24 refs., 7 figs., 1 tab.

  5. Enhanced Corrosion Resistance of Iron-Based Amorphous Alloys

    SciTech Connect

    Rebak, R B; Day, S D; Lian, T; Aprigliano, L F; Hailey, P D; Farmer, J C

    2007-02-18

    Iron-based amorphous alloys possess enhanced hardness and are highly resistant to corrosion, which make them desirable for wear applications in corrosive environments. It was of interest to examine the behavior of amorphous alloys during anodic polarization in concentrated salt solutions and in the salt-fog testing. Results from the testing of one amorphous material (SAM2X5) both in ribbon form and as an applied coating are reported here. Cyclic polarization tests were performed on SAM2X5 ribbon as well as on other nuclear engineering materials. SAM2X5 showed the highest resistance to localized corrosion in 5 M CaCl{sub 2} solution at 105 C. Salt fog tests of 316L SS and Alloy 22 coupons coated with amorphous SAM2X5 powder showed resistance to rusting. Partial devitrification may be responsible for isolated pinpoint rust spots in some coatings.

  6. Nitrogen assimilation from amorphous detritus by two coastal consumers

    NASA Astrophysics Data System (ADS)

    D'Avanzo, Charlene; Alber, Merryl; Valiela, Ivan

    1991-08-01

    The food value of recognizable pieces of dead vegetation, morphous detritus, has been the focus of many studies in coastal systems. In contrast, the nutritional quality and formation process of amorphous detritus, aggregates of dissolved organic matter (DOM), is poorly studied. We created 15N-labelled aggregates from the leachate of four macrophytes, a marsh grass and three macroalgae common in New England coastal waters. We fed the labelled aggregates to two coastal consumers, the grass shrimp Palaemonetes pugio and the sheepshead minnow Cyprinodon variegatus. Fish and shrimp fed each of the labelled aggregates became labelled with 15N. This study provides direct evidence for nitrogen assimilation from amorphous detritus by marine consumers. In addition, fish fed amorphous marsh grass detritus assimilated 10-40 times more nitrogen from this detritus than from morphous grass detritus. Therefore, amorphous aggregates may be higher-quality food than morphous detrital fragments for coastal consumers.

  7. Properties of vacuum arc deposited amorphous hard carbon films

    SciTech Connect

    Anders, S.; Anders, A.; Raoux, S.

    1995-04-01

    Amorphous hard carbon films formed by vacuum arc deposition are hydrogen-free, dense, and very hard. The properties of amorphous hard carbon films depend strongly on the energy of the incident ions. A technique which is called Plasma Immersion Ion Implantation can be applied to vacuum arc deposition of amorphous hard carbon films to influence the ion energy. The authors have studied the influence of the ion energy on the elastic modulus determined by an ultrasonic method, and have measured the optical gap for films with the highest sp{sup 3} content they have obtained so far with this deposition technique. The results show an elastic modulus close to that of diamond, and an optical gap of 2.1 eV which is much greater than for amorphous hard carbon films deposited by other techniques.

  8. Amorphous solid dispersions: Rational selection of a manufacturing process.

    PubMed

    Vasconcelos, Teófilo; Marques, Sara; das Neves, José; Sarmento, Bruno

    2016-05-01

    Amorphous products and particularly amorphous solid dispersions are currently one of the most exciting areas in the pharmaceutical field. This approach presents huge potential and advantageous features concerning the overall improvement of drug bioavailability. Currently, different manufacturing processes are being developed to produce amorphous solid dispersions with suitable robustness and reproducibility, ranging from solvent evaporation to melting processes. In the present paper, laboratorial and industrial scale processes were reviewed, and guidelines for a rationale selection of manufacturing processes were proposed. This would ensure an adequate development (laboratorial scale) and production according to the good manufacturing practices (GMP) (industrial scale) of amorphous solid dispersions, with further implications on the process validations and drug development pipeline. PMID:26826438

  9. Amorphous calcium phosphates for tooth mineralization.

    PubMed

    Tung, Ming S; Eichmiller, Frederick C

    2004-09-01

    The destruction of tooth structure through caries and erosive processes is due to two types of acidic challenges that affect the tooth in different ways. Acidic attack by cariogenic bacteria initially produces subsurface lesions that weaken the enamel and, if left unchecked, can progress through the enamel and dentin and eventually into the pulpal cavity. Erosive attack by acidic foods and beverages removes mineral from the surface of enamel and initially causes dulling and loss of tooth luster; if left unchecked, it can progress to a more severe loss of enamel thickness and contour. This article focuses on the potential means of improving the cosmetic appearance of teeth by depositing mineral into surface defects. Several approaches use the unique properties of amorphous calcium phosphate (ACP) compounds, which have the highest rates of formation and dissolution among all the calcium phosphates. ACP has been shown to rapidly hydrolyze to form apatite, similar to carbonated apatite, the tooth mineral. Products containing ACP or ingredients that form ACP can include toothpastes, mouth rinses, artificial saliva, chewing gums, topically applied coatings, and other vehicles for topical use. When applied, they readily precipitate ACPs on and into tooth-surface defects. These products hopefully will provide users with new tools to restore and enhance the smoothness and luster of their teeth.

  10. Inversion of diffraction data for amorphous materials

    PubMed Central

    Pandey, Anup; Biswas, Parthapratim; Drabold, D. A.

    2016-01-01

    The general and practical inversion of diffraction data–producing a computer model correctly representing the material explored–is an important unsolved problem for disordered materials. Such modeling should proceed by using our full knowledge base, both from experiment and theory. In this paper, we describe a robust method to jointly exploit the power of ab initio atomistic simulation along with the information carried by diffraction data. The method is applied to two very different systems: amorphous silicon and two compositions of a solid electrolyte memory material silver-doped GeSe3. The technique is easy to implement, is faster and yields results much improved over conventional simulation methods for the materials explored. By direct calculation, we show that the method works for both poor and excellent glass forming materials. It offers a means to add a priori information in first-principles modeling of materials, and represents a significant step toward the computational design of non-crystalline materials using accurate interatomic interactions and experimental information. PMID:27652893

  11. Electron and hole dynamics in amorphous silicon

    SciTech Connect

    Werner, A.; Kunst, M.

    1988-07-01

    Charge carrier dynamics in doped and undoped hydrogenated amorphous silicon (a-Si:H) films is studied by contactless time-resolved photoconductivity measurements. Subband-gap and above band-gap excitation are used to generate excess mobile charge carriers. In undoped a-Si:H the electron decay at charge carrier concentrations larger than 10/sup 16/ cm/sup -3/ is mainly due to an electron-hole recombination which is controlled by hole dispersion. n doping introduces hole traps which increase the effective electron lifetime drastically as they quench this electron-hole recombination channel. At high n-doping levels the electron decay becomes faster due to an increase of the concentration of recombination centers upon doping. In lightly doped p-type samples the transient photoconductivity reflects the interaction of mobile holes with states in the valence-band tail. In heavily doped p- and n-type films the majority carriers decay by a second-order recombination process with trapped minority charge carriers. The transport parameters deduced agree with time-of-flight data.

  12. Reversible Avalanches and Criticality in Amorphous Solids

    NASA Astrophysics Data System (ADS)

    Reichhardt, Charles

    2015-03-01

    Despite its importance for basic science and industry, the physical process that causes a solid to change its shape permanently under external deformation is still not well understood. In this paper we use molecular dynamics simulations of amorphous solids under oscillatory shear to study this phenomenon, and show that at a critical strain amplitude, the size of the cooperative atomic motion that allows for a permanent deformation diverges. We compare this non-equilibrium critical behavior to that of a ``front depinning'' transition. This viewpoint, based on fluctuations and statistics, is complementary to the dynamical ``transition to chaos'' which was previously identified at the same strain amplitude. Below this irreversibile-depinning transition, we observe large avalanches which are completely repetitive with each shear strain cycle. This suggests that while avalanches on their own do not cause irreversible deformation, it is likely that the irreversibility transition and the ``depinning-like'' transition are two aspects of the same phenomena. One implication is that the transition could be detected before the onset of irreversible flow by an analysis of the power spectra of avalanches. Work done in collaboration with Ido Regev, Karin Dahmen, John Weber, and Turab Lookman.

  13. Ferromagnetic resonance in submicron amorphous wires

    NASA Astrophysics Data System (ADS)

    Kraus, Luděk; Frait, Zdeněk; Ababei, Gabriel; Chayka, Oleksandr; Chiriac, Horia

    2012-03-01

    Ferromagnetic resonance in glass-coated amorphous wires with the diameter of metallic core varying from 25 μm to 133 nm is investigated. The microwave frequencies of 49.1 and 69.7 GHz are used and static magnetic field is applied either parallel or perpendicular to the long wire axis. In agreement with theoretical predictions the resonance curves of submicron wires substantially differ from the curves of the bulk wires. Depending on the symmetry and intensity of microwave electric and magnetic fields in the sample vicinity the circumferential and/or dipolar resonance modes can be excited. In bulk wires the resonance fields of the two modes coincide. In submicron wires, however, their resonance fields differ, indicating the metallic character of the circumferential mode and the insulator character of the dipolar mode. In wires with diameters 717 and 869 nm radial standing spin wave resonances are observed in parallel field configuration. The experimental results for the parallel field configuration can be well explained by the rigorous theoretical model. From the fit of experimental data the exchange stiffness constant A = 8.2 10-12 J/m and perpendicular surface anisotropy constant Ks = 6 × 10-4 J/m2 are obtained. The resonance curves measured in the transversal field configuration can be well explained in the frame of the skin effect and quasistatic approximations for the bulk and submicron wires, respectively. In submicron wires, however, an additional resonance of unknown origin is observed at higher magnetic fields.

  14. Disordered amorphous calcium carbonate from direct precipitation

    SciTech Connect

    Farhadi Khouzani, Masoud; Chevrier, Daniel M.; Güttlein, Patricia; Hauser, Karin; Zhang, Peng; Hedin, Niklas; Gebauer, Denis

    2015-06-01

    Amorphous calcium carbonate (ACC) is known to play a prominent role in biomineralization. Different studies on the structure of biogenic ACCs have illustrated that they can have distinct short-range orders. However, the origin of so-called proto-structures in synthetic and additive-free ACCs is not well understood. In the current work, ACC has been synthesised in iso-propanolic media by direct precipitation from ionic precursors, and analysed utilising a range of different techniques. The data suggest that this additive-free type of ACC does not resemble clear proto-structural motifs relating to any crystalline polymorph. This can be explained by the undefined pH value in iso-propanolic media, and the virtually instantaneous precipitation. Altogether, this work suggests that aqueous systems and pathways involving pre-nucleation clusters are required for the generation of clear proto-structural features in ACC. Experiments on the ACC-to-crystalline transformation in solution with and without ethanol highlight that polymorph selection is under kinetic control, while the presence of ethanol can control dissolution re-crystallisation pathways.

  15. Disordered amorphous calcium carbonate from direct precipitation

    DOE PAGES

    Farhadi Khouzani, Masoud; Chevrier, Daniel M.; Güttlein, Patricia; Hauser, Karin; Zhang, Peng; Hedin, Niklas; Gebauer, Denis

    2015-06-01

    Amorphous calcium carbonate (ACC) is known to play a prominent role in biomineralization. Different studies on the structure of biogenic ACCs have illustrated that they can have distinct short-range orders. However, the origin of so-called proto-structures in synthetic and additive-free ACCs is not well understood. In the current work, ACC has been synthesised in iso-propanolic media by direct precipitation from ionic precursors, and analysed utilising a range of different techniques. The data suggest that this additive-free type of ACC does not resemble clear proto-structural motifs relating to any crystalline polymorph. This can be explained by the undefined pH value inmore » iso-propanolic media, and the virtually instantaneous precipitation. Altogether, this work suggests that aqueous systems and pathways involving pre-nucleation clusters are required for the generation of clear proto-structural features in ACC. Experiments on the ACC-to-crystalline transformation in solution with and without ethanol highlight that polymorph selection is under kinetic control, while the presence of ethanol can control dissolution re-crystallisation pathways.« less

  16. Amorphous Alloy Surpasses Steel and Titanium

    NASA Technical Reports Server (NTRS)

    2004-01-01

    In the same way that the inventions of steel in the 1800s and plastic in the 1900s sparked revolutions for industry, a new class of amorphous alloys is poised to redefine materials science as we know it in the 21st century. Welcome to the 3rd Revolution, otherwise known as the era of Liquidmetal(R) alloys, where metals behave similar to plastics but possess more than twice the strength of high performance titanium. Liquidmetal alloys were conceived in 1992, as a result of a project funded by the California Institute of Technology (CalTech), NASA, and the U.S. Department of Energy, to study the fundamentals of metallic alloys in an undercooled liquid state, for the development of new aerospace materials. Furthermore, NASA's Marshall Space Flight Center contributed to the development of the alloys by subjecting the materials to testing in its Electrostatic Levitator, a special instrument that is capable of suspending an object in midair so that researchers can heat and cool it in a containerless environment free from contaminants that could otherwise spoil the experiment.

  17. Amorphous Silicon: Flexible Backplane and Display Application

    NASA Astrophysics Data System (ADS)

    Sarma, Kalluri R.

    Advances in the science and technology of hydrogenated amorphous silicon (a-Si:H, also referred to as a-Si) and the associated devices including thin-film transistors (TFT) during the past three decades have had a profound impact on the development and commercialization of major applications such as thin-film solar cells, digital image scanners and X-ray imagers and active matrix liquid crystal displays (AMLCDs). Particularly, during approximately the past 15 years, a-Si TFT-based flat panel AMLCDs have been a huge commercial success. a-Si TFT-LCD has enabled the note book PCs, and is now rapidly replacing the venerable CRT in the desktop monitor and home TV applications. a-Si TFT-LCD is now the dominant technology in use for applications ranging from small displays such as in mobile phones to large displays such as in home TV, as well-specialized applications such as industrial and avionics displays.

  18. Oxygenated amorphous carbon for resistive memory applications

    NASA Astrophysics Data System (ADS)

    Santini, Claudia A.; Sebastian, Abu; Marchiori, Chiara; Jonnalagadda, Vara Prasad; Dellmann, Laurent; Koelmans, Wabe W.; Rossell, Marta D.; Rossel, Christophe P.; Eleftheriou, Evangelos

    2015-10-01

    Carbon-based electronics is a promising alternative to traditional silicon-based electronics as it could enable faster, smaller and cheaper transistors, interconnects and memory devices. However, the development of carbon-based memory devices has been hampered either by the complex fabrication methods of crystalline carbon allotropes or by poor performance. Here we present an oxygenated amorphous carbon (a-COx) produced by physical vapour deposition that has several properties in common with graphite oxide. Moreover, its simple fabrication method ensures excellent reproducibility and tuning of its properties. Memory devices based on a-COx exhibit outstanding non-volatile resistive memory performance, such as switching times on the order of 10 ns and cycling endurance in excess of 104 times. A detailed investigation of the pristine, SET and RESET states indicates a switching mechanism based on the electrochemical redox reaction of carbon. These results suggest that a-COx could play a key role in non-volatile memory technology and carbon-based electronics.

  19. Inversion of diffraction data for amorphous materials

    NASA Astrophysics Data System (ADS)

    Pandey, Anup; Biswas, Parthapratim; Drabold, D. A.

    2016-09-01

    The general and practical inversion of diffraction data–producing a computer model correctly representing the material explored–is an important unsolved problem for disordered materials. Such modeling should proceed by using our full knowledge base, both from experiment and theory. In this paper, we describe a robust method to jointly exploit the power of ab initio atomistic simulation along with the information carried by diffraction data. The method is applied to two very different systems: amorphous silicon and two compositions of a solid electrolyte memory material silver-doped GeSe3. The technique is easy to implement, is faster and yields results much improved over conventional simulation methods for the materials explored. By direct calculation, we show that the method works for both poor and excellent glass forming materials. It offers a means to add a priori information in first-principles modeling of materials, and represents a significant step toward the computational design of non-crystalline materials using accurate interatomic interactions and experimental information.

  20. High performance amorphous selenium lateral photodetector

    NASA Astrophysics Data System (ADS)

    Abbaszadeh, Shiva; Allec, Nicholas; Karim, Karim S.

    2012-03-01

    Lateral amorphous selenium (a-Se) detectors based on the metal-semiconductor-metal (MSM) device structure have been studied for indirect detector medical imaging applications. These detectors have raised interest due to their simple structure, ease of fabrication, high-speed, low dark current, low capacitance per unit area and better light utilization. The lateral device structure has a benefit that the electrode spacing may be easily controlled to reduce the required bias for a given desired electric field. In indirect conversion x-ray imaging, the scintillator is coupled to the top of the a-Se MSM photodetector, which itself is integrated on top of the thin-film-transistor (TFT) array. The carriers generated at the top surface of the a-Se layer experience a field that is parallel to the surface, and does not initially sweep them away from the surface. Therefore these carriers may recombine or get trapped in surface states and change the field at the surface, which may degrade the performance of the photodetector. In addition, due to the finite width of the electrodes, the fill factor of the device is less than unity. In this study we examine the effect of lateral drift of carriers and the fill factor on the photodetector performance. The impact of field magnitude on the performance is also investigated.

  1. Breakdown analysis of multilayer amorphous silicon photoreceptors

    NASA Astrophysics Data System (ADS)

    Hu, Jian

    1993-06-01

    The breakdown mechanism of hydrogenated amorphous silicon (a-Si:H) has been investigated. It has been shown that the acceptance of the surface potential of an a-Si:H photoreceptor is very sensitive to the micro-roughness of the substrate surface. This is because the junction between the metal substrate (usually aluminum) and the blocking layer (p+ or n+ a-Si:H) is strongly affected by the micro-roughness of the substrate surface. A model is proposed to expound this phenomenon, which indicates that the existence of micro- defects on the substrate surface results in the bending of the metal-semiconductor junction at these defect positions; that is, the original parallel plane junction changes into a spherical abrupt junction. Compared to the former, the curved junction has a lower breakdown voltage, therefore, it will more easily break down at these defect positions during charging. An a-Si:H photoreceptor was prepared on the drum substrate half covered with a thin aluminum film to confirm the model. The experiment result was qualitatively in agreement with the analysis mentioned above. In addition, the effects of PVD-like deposition processes (e.g., high power or high argon diluted silane deposition) on the microstructure and breakdown of a-Si:H photoreceptors are reviewed.

  2. Conductance fluctuations in hydrogenated amorphous silicon

    SciTech Connect

    Parman, C.E.

    1992-01-01

    Measurements of co-planar resistance fluctuations are reported for n-type doped hydrogenated amorphous silicon over the temperature range 190 < T < 450 K. The spectral density of the fluctuations obey a 1/f frequency dependence over the frequency range 1 < f < 10[sup 3] Hz. The noise power displays a non-linear dependence on the applied DC current, that is that noise power S[sub I] [proportional to] I[sup b], where 1.0 < b < 2.5. Random telegraph switching noise is observed with fluctuations as large as [delta]R/R [approx] 10[sup [minus]2] in samples with volumes of 10[sup [minus]7] cm[sup 3]. Statistical analysis of the noise power spectra show the fluctuations to be strongly non-Gaussian. The noise power magnitude and frequency dependence are both time dependent. These results suggest that cooperative dynamics govern the conductance fluctuations, and are discussed in terms of models for noise in composite and inhomogeneous materials.

  3. How does an amorphous surface influence molecular binding?--ovocleidin-17 and amorphous calcium carbonate.

    PubMed

    Freeman, Colin L; Harding, John H; Quigley, David; Rodger, P Mark

    2015-07-14

    Atomistic molecular dynamics simulations of dehydrated amorphous calcium carbonate interacting with the protein ovocleidin-17 are presented. These simulations demonstrate that the amorphisation of the calcium carbonate surface removes water structure from the surface. This reduction of structure allows the protein to bind with many residues, unlike on crystalline surfaces where binding is strongest when only a few residues are attached to the surface. Basic residues are observed to dominate the binding interactions. The implications for protein control over crystallisation are discussed. PMID:26009013

  4. Amorphous silicon-carbon alloys and amorphous carbon from direct methane and ethylene activation by ECR

    SciTech Connect

    Conde, J.P.; Chu, V.; Giorgis, F.; Pirri, C.F.; Arekat, S.

    1997-07-01

    Hydrogenated amorphous silicon-carbon alloys are prepared using electron-cyclotron resonance (ECR) plasma-enhanced chemical vapor deposition. Hydrogen is introduced into the source resonance cavity as an excitation gas. Silane is introduced in the main chamber in the vicinity of the plasma stream, whereas the carbon source gases, methane or ethylene, are introduced either with the silane or with the hydrogen as excitation gases. The effect of the type of carbon-source gas, excitation gas mixture and silane-to-carbon source gas flow ratio on the deposition rate, bandgap, subgap density of states, spin density and hydrogen evolution are studied.

  5. Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films

    SciTech Connect

    Hellman, Frances

    1998-10-03

    OAK B204 Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films. The work in the past 6 months has involved three areas of magnetic thin films: (1) amorphous rare earth-transition metal alloys, (2) epitaxial Co-Pt and hTi-Pt alloy thin films, and (3) collaborative work on heat capacity measurements of magnetic thin films, including nanoparticles and CMR materials.

  6. Structure and Properties of Amorphous Transparent Conducting Oxides

    NASA Astrophysics Data System (ADS)

    Medvedeva, Julia

    Driven by technological appeal, the research area of amorphous oxide semiconductors has grown tremendously since the first demonstration of the unique properties of amorphous indium oxide more than a decade ago. Today, amorphous oxides, such as a-ITO, a-IZO, a-IGZO, or a-ZITO, exhibit the optical, electrical, thermal, and mechanical properties that are comparable or even superior to those possessed by their crystalline counterparts, pushing the latter out of the market. Large-area uniformity, low-cost low-temperature deposition, high carrier mobility, optical transparency, and mechanical flexibility make these materials appealing for next-generation thin-film electronics. Yet, the structural variations associated with crystalline-to-amorphous transition as well as their role in carrier generation and transport properties of these oxides are far from being understood. Although amorphous oxides lack grain boundaries, factors like (i) size and distribution of nanocrystalline inclusions; (ii) spatial distribution and clustering of incorporated cations in multicomponent oxides; (iii) formation of trap defects; and (iv) piezoelectric effects associated with internal strains, will contribute to electron scattering. In this work, ab-initio molecular dynamics (MD) and accurate density-functional approaches are employed to understand how the properties of amorphous ternary and quaternary oxides depend on quench rates, cation compositions, and oxygen stoichiometries. The MD results, combined with thorough experimental characterization, reveal that interplay between the local and long-range structural preferences of the constituent oxides gives rise to a complex composition-dependent structural behavior in the amorphous oxides. The proposed network models of metal-oxygen polyhedra help explain the observed intriguing electrical and optical properties in In-based oxides and suggest ways to broaden the phase space of amorphous oxide semiconductors with tunable properties. The

  7. Amorphization and anisotropy effects on a ferromagnetic bilayer system

    NASA Astrophysics Data System (ADS)

    Bengrine, M.; Benyoussef, A.; El Kenz, A.; Mhirech, F.; Peliti, L.

    1999-07-01

    A ferromagnetic amorphous bilayer system, consisting of two magnetic monolayers (A and B) with spins ( S A= {1}/{2} and S B= {3}/{2}) and different interaction constants coupled together with interlayer coupling, is studied by the use of effective field theory. In addition to the influence of crystal field interaction the effects of the amorphization in the monolayer B and in the interlayer coupling give some interesting phenomena in the system. Phase diagrams and magnetization are investigated in detail.

  8. Crystallization Behaviour of Amorphous Al-Ni-Nd Alloy

    SciTech Connect

    Goegebakan, Musa; Guendes, Alaaddin

    2007-04-23

    In this study, crystallization behaviour of rapidly solidified Al85Ni5Nd10 alloy has been investigated by differential scanning calorimetry (DSC). Continuous heating DSC trace of amorphous Al85Ni5Nd10 alloy consisted of three exothermic peaks. This indicated that; crystallization of amorphous Al85Ni5Nd10 alloy during continous heating takes places in three stages. Before the first exothermic peak, a glass transition temperature was observed.

  9. Effect of counterions on the properties of amorphous atorvastatin salts.

    PubMed

    Sonje, Vishal M; Kumar, Lokesh; Puri, Vibha; Kohli, Gunjan; Kaushal, Aditya M; Bansal, Arvind K

    2011-11-20

    Amorphous systems have gained importance as a tool for addressing delivery challenges of poorly water soluble drugs. A careful assessment of thermodynamic and kinetic behavior of amorphous form is necessary for successful use of amorphous form in drug delivery. The present study was undertaken to evaluate effect of monovalent sodium (Na(+); ATV Na), and bivalent calcium (Ca(2+); ATV Ca) and magnesium (Mg(2+); ATV Mg) counterions on properties of amorphous salts of atorvastatin (ATV) model drug. Amorphous form was generated from crystalline salts of ATV by spray drying, and characterized for glass transition temperature (T(g)), fragility and devitrification tendency. In addition, chemical stability of the amorphous salt forms was evaluated. Fragility was studied by calculating activation enthalpy for structural relaxation at T(g), from heating rate dependency of T(g). Density functional theory and relative pK(a)'s of counterions were evaluated to substantiate trend in glass transition temperature. T(g) of salts followed order: ATV Ca>ATV Mg>ATV Na. All salts were fragile to moderately fragile, with D value ranging between 9 and 16. Ease of devitrification followed the order: ATV Na∼ATV Mg≫ATV Ca, using isothermal crystallization and reduced crystallization temperature method. Chemical stability at 80°C showed higher degradation of amorphous ATV Ca (∼5%), while ATV Na and ATV Mg showed degradation of 1-2%. Overall, ATV Ca was better in terms of glass forming ability, higher T(g) and physical stability. The study has importance in selection of a suitable amorphous form, during early drug development phase. PMID:21907794

  10. Thermal Properties of Amorphous Al-Ni-Si Alloy

    SciTech Connect

    Goegebakan, Musa; Okumus, Mustafa

    2007-04-23

    Thermal properties of the amorphous phases in rapidly solidified Al70Ni13Si17 alloy has been investigated by a combination of differential scanning calorimetry DSC. During continuous heating, three exothermic crystallization peaks were observed. Activation energies for the three crystallization peaks were calculated by the Kissinger and Ozawa methods give good agreement. This study describes the thermal properties of rapidly solidified Al70Ni13Si17 amorphous alloy.

  11. Threshold irradiation dose for amorphization of silicon carbide

    SciTech Connect

    Snead, L.L.; Zinkle, S.J.

    1997-04-01

    The amorphization of silicon carbide due to ion and electron irradiation is reviewed with emphasis on the temperature-dependent critical dose for amorphization. The effect of ion mass and energy on the threshold dose for amorphization is summarized, showing only a weak dependence near room temperature. Results are presented for 0.56 MeV silicon ions implanted into single crystal 6H-SiC as a function of temperature and ion dose. From this, the critical dose for amorphization is found as a function of temperature at depths well separated from the implanted ion region. Results are compared with published data generated using electrons and xenon ions as the irradiating species. High resolution TEM analysis is presented for the Si ion series showing the evolution of elongated amorphous islands oriented such that their major axis is parallel to the free surface. This suggests that surface of strain effects may be influencing the apparent amorphization threshold. Finally, a model for the temperature threshold for amorphization is described using the Si ion irradiation flux and the fitted interstitial migration energy which was found to be {approximately}0.56 eV. This model successfully explains the difference in the temperature-dependent amorphization behavior of SiC irradiated with 0.56 MeV silicon ions at 1 x 10{sup {minus}3} dpa/s and with fission neutrons irradiated at 1 x 10{sup {minus}6} dpa/s irradiated to 15 dpa in the temperature range of {approximately}340 {+-} 10K.

  12. Structural and Magnetic Properties of Ni Rich Amorphous Boride Nanoparticles

    SciTech Connect

    Singh, Vidyadhar; Banerjee, Progna; Srinivas, V.; Babu, N. H.

    2011-06-30

    The Ni rich amorphous boride nanoparticles can be prepared very easily by the solid-solid reaction of the NiCl{sub 2} and NaBH{sub 4} powders at room temperature. XRD, DTA-TG, FESEM, TEM, and selected-area electron diffraction characterize the resultant nanoparticles. The results show that the resultant is mainly composed of the amorphous Ni-B alloy nanoparticles with an average diameter of 15-25 nm.

  13. 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.

  14. 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.

  15. Pharmaceutical micro-particles give amorphous sucrose higher physical stability.

    PubMed

    Hellrup, Joel; Mahlin, Denny

    2011-05-16

    The aim of this study was to explore how pharmaceutical micro-sized filler particles affect the amorphous stability of sucrose in sucrose/filler particle composites produced by freeze-drying. Focus was put on the filler particles' properties crystallinity, hygroscopicity, hydrophobicity, and surface area, and their influence on physical stability of the amorphous phase. The micro-sized filler particles were examined with Blaine permeametry, gas adsorption, pycnometry, gravimetric vapour sorption, X-ray diffraction, and light microscopy before composites of sucrose and micro-sized filler particles were prepared by freeze-drying. The stability of the composites was examined with X-ray diffraction, differential scanning calorimetry (DSC), and microcalorimetry. All composites were amorphous and showed higher stability compared to pure amorphous sucrose, which was evident from a delay in heat and moisture-induced crystallization. However, calcium carbonate and oxazepam micro-sized filler particles lost their ability to stabilize the amorphous sucrose when exposed to humidity. The dry glass transition temperature (T(g)) was higher for the composites, indicating the stabilization was mediated by a reduced molecular mobility of the amorphous phase. PMID:21356288

  16. Structural Properties of Amorphous Indium-Based Oxides

    NASA Astrophysics Data System (ADS)

    Khanal, Rabi; Medvedeva, Julia

    2014-03-01

    Amorphous transparent conducting and semiconducting oxides exhibit similar or even superior properties to those observed in their crystalline counterparts. To understand how the structural properties change upon amorphization and how chemical composition affects the local and long-range structure of the amorphous oxides, we employ first-principles molecular dynamics to generate amorphous In-X-O with X =Zn, Ga, Sn, Ge, Y, or Sc, and compare their local structure features to those obtained for amorphous and crystalline indium oxide. The results reveal that the short-range structure of the Metal-O polyhedra is generally preserved in the amorphous oxides; however, different metals (In and X) show quantitatively or qualitatively different behavior. Some of the metals retain their natural distances and/or coordination; while others allow for a highly distorted environment and thus favor ``defect'' formation under variable oxygen conditions. At the same time, we find that the presence of X increases both the average In-O coordination and the number of the 6-coordinated In atoms as compared to those in IO. The improved In coordination may be responsible for the observed reduction in the carrier concentration as the substitution level in In-X-O increases.

  17. Variable-amplitude oscillatory shear response of amorphous materials

    NASA Astrophysics Data System (ADS)

    Perchikov, Nathan; Bouchbinder, Eran

    2014-06-01

    Variable-amplitude oscillatory shear tests are emerging as powerful tools to investigate and quantify the nonlinear rheology of amorphous solids, complex fluids, and biological materials. Quite a few recent experimental and atomistic simulation studies demonstrated that at low shear amplitudes, an amorphous solid settles into an amplitude- and initial-conditions-dependent dissipative limit cycle, in which back-and-forth localized particle rearrangements periodically bring the system to the same state. At sufficiently large shear amplitudes, the amorphous system loses memory of the initial conditions, exhibits chaotic particle motions accompanied by diffusive behavior, and settles into a stochastic steady state. The two regimes are separated by a transition amplitude, possibly characterized by some critical-like features. Here we argue that these observations support some of the physical assumptions embodied in the nonequilibrium thermodynamic, internal-variables based, shear-transformation-zone model of amorphous viscoplasticity; most notably that "flow defects" in amorphous solids are characterized by internal states between which they can make transitions, and that structural evolution is driven by dissipation associated with plastic deformation. We present a rather extensive theoretical analysis of the thermodynamic shear-transformation-zone model for a variable-amplitude oscillatory shear protocol, highlighting its success in accounting for various experimental and simulational observations, as well as its limitations. Our results offer a continuum-level theoretical framework for interpreting the variable-amplitude oscillatory shear response of amorphous solids and may promote additional developments.

  18. Effect of different "states" of sorbed water on amorphous celecoxib.

    PubMed

    Shete, Ganesh; Kuncham, Swathi; Puri, Vibha; Gangwal, Rahul P; Sangamwar, Abhay T; Bansal, Arvind Kumar

    2014-07-01

    Glass transition temperature (Tg) of an amorphous drug is a vital physical phenomenon that influences its visco-elastic properties, physical, and chemical stability. Water acts as a plasticizer for amorphous drugs thus increasing their recrystallization kinetics. This reduces the solubility advantage of an amorphous drug. Hence, there is an interest in understanding the relationship between water content and Tg of amorphous drug. We have studied the effect of "state" of sorbed water on Tg of amorphous celecoxib (ACLB). ACLB was allowed to sorb water at relative humidity of 33%, 53%, 75%, and 93%. ALCB showed biphasic sorption of water designated as "bound" and "solvent-like" state of water associated with ACLB. Molecular modeling studies provided deeper insights into the interaction of water with ACLB. A distinct co-relationship between the state of water and its plasticization capacity was observed. Bound state of water had a very profound effect on the fall in experimentally observed Tg (T(g-exp)) value. Solvent-like state of water had little impact on T(g-exp) value. Tg of ACLB-water mixture was predicted by Gordon-Taylor equation (T(g-pre)). The deviations in T(g-exp) and Tg-pre were correlated to volume non-additivity and non-ideal mixing. This study has implications on the development of formulations based on amorphous forms. PMID:24801826

  19. Structures and Low-Energy Excitations of Amorphous Gas Hydrates

    NASA Astrophysics Data System (ADS)

    Kikuchi, Tatsuya; Inamura, Yasuhiro; Onoda-Yamamuro, Noriko; Yamamuro, Osamu

    2012-09-01

    We have prepared amorphous clathrate hydrates of Ar, CD4, Xe, and SF6 by depositing mixed vapors of water and guest molecules on a substrate at ca. 10 K. The structure and vibrational density of states were investigated by neutron diffraction and inelastic scattering techniques, respectively. The radial distribution functions of the amorphous hydrates are larger than that of pure amorphous ice in the region around 4 Å (the center-edge distance of the 12-hedral cage), indicating that a local cagelike structure is maintained even in the amorphous solids. The incorporation of the guest molecules decreases the intensity of the phonon excitation below 7 meV, which is known as a low-energy excitation characteristic of amorphous ice. This may be due to the effect that the disorder, defects and distortion producing the low-energy excitation are reduced by a hydrophobic hydration between the guest and water molecules and the resultant hydrogen-bond formation. A similar effect was also observed in the libration mode of water molecules at about 60 meV. The present work has revealed the relation among the local cage formation, hydrogen bonds, and low energy excitations in amorphous hydrates that is the simplest hydrophobic hydration system (H2O--gas mixture).

  20. Deformation-Induced Amorphization of Copper-Titanium Intermetallics

    NASA Astrophysics Data System (ADS)

    Askenazy, Philip Douglas

    Two methods of inducing amorphization in Cu-Ti intermetallic compounds by mechanical means have been investigated. Ingots of compositions Cu_{35}Ti _{65} and Cu_ {33.3}Ti_{66.7} were rapidly quenched into ribbons. The microstructure consisted largely of microcrystals in an amorphous matrix, which were either quenched in or grown by annealing. The ribbons were cold-rolled, which reduced their effective thickness by a factor of about 8. The status of the intermetallic compound CuTi_2 was monitored by x-ray diffraction and transmission electron microscopy (TEM). The crystals were found to amorphize as rolling progressed. This behavior was not reproduced in polycrystalline samples that had no amorphous matrix present initially. The presence of the amorphous phase is thus necessary for amorphization of the crystal: it eliminates the need to nucleate the new glass, and it prevents the ribbon from disintegrating at high deformation stages. It may also change the deformation mechanism that occurs in the crystals, retarding the onset of amorphization. Diffuse scattering in close-packed directions is similar to that seen in electron irradiation experiments. It is postulated that the chemical disorder present in antiphase boundaries caused by deformation raises the free energy of the crystal higher than that of the amorphous phase. Ingots of the same compound were worn against each other in a custom-built wear apparatus. The design eliminates iron contamination of the wear sample and requires relatively small quantities of material. Alteration of the surface structure was monitored by plane-view and cross -sectional TEM. Larger subsurface crystals exhibit diffuse scattering, similar to that found in the rolled samples. A wide range of grain sizes was observed, due to the inhomogeneous nature of the wear process. An unusual phase was observed at the surface, consisting of a nanometer-scale mixture of aligned nanocrystalline regions and disordered areas. Some amorphous phase is

  1. Amorphous silicon x-ray image sensor

    NASA Astrophysics Data System (ADS)

    Chabbal, Jean; Chaussat, Christophe; Ducourant, Thierry; Fritsch, Lionel; Michailos, Jean; Spinnler, Vincent; Vieux, Gerard; Arques, Marc; Hahm, Gerhard; Hoheisel, Martin; Horbaschek, Heinz; Schulz, Reiner F.; Spahn, Martin F.

    1996-04-01

    The design and the performance of a 20 cm by 20 cm flat panel x-ray detector for digital radiography and fluoroscopy is described: Thin film amorphous silicon (aSi) technology has been used to build a 1024 by 1024 photodetector matrix, each pixel including both a photodiode and a switching diode; the pixel size is 196 by 196 micrometers2. A high resolution and high absorption CsI(Tl) scintillator layer covers the top of the photodetector matrix in order to provide for x ray to light conversion. For low electronic noise and 30 fr/s operating rate we developed a custom design charge readout integrated circuit. The detector delivers a 12 bit digital output. The image quality, signal to noise ratio, and DQE are presented and discussed. The flat panel detector provides a MTF in excess of 30% at 2 lp/mm and a high contrast ratio without any distortion on the whole imaging area. The x-ray absorption is 70% for 50 KeV photons. The readout amplifier is optimized to reduce the electronic noise down to 1000 e-. This low noise level, combined with high sensitivity (1150 e-/incident x-ray quantum) provides the capability for fluoroscopic applications. The digital flat panel detector has been integrated in a C-arm system for cardiology and has been used on a regular basis in a European hospital since February 1995. The results are discussed for several operating modes: radiography and fluoroscopy. Conclusions on present detector performances, as well as further improvements, are presented.

  2. Amorphous phase formation in mechanically alloyed iron-based systems

    NASA Astrophysics Data System (ADS)

    Sharma, Satyajeet

    Bulk metallic glasses have interesting combination of physical, chemical, mechanical, and magnetic properties which make them attractive for a variety of applications. Consequently there has been a lot of interest in understanding the structure and properties of these materials. More varied applications can be sought if one understands the reasons for glass formation and the methods to control them. The glass-forming ability (GFA) of alloys can be substantially increased by a proper selection of alloying elements and the chemical composition of the alloy. High GFA will enable in obtaining large section thickness of amorphous alloys. Ability to produce glassy alloys in larger section thicknesses enables exploitation of these advanced materials for a variety of different applications. The technique of mechanical alloying (MA) is a powerful non-equilibrium processing technique and is known to produce glassy (or amorphous) alloys in several alloy systems. Metallic amorphous alloys have been produced by MA starting from either blended elemental metal powders or pre-alloyed powders. Subsequently, these amorphous alloy powders could be consolidated to full density in the temperature range between the glass transition and crystallization temperatures, where the amorphous phase has a very low viscosity. This Dissertation focuses on identifying the various Fe-based multicomponent alloy systems that can be amorphized using the MA technique, studying the GFA of alloys with emphasis on improving it, and also on analyzing the effect of extended milling time on the constitution of the amorphous alloy powder produced at earlier times. The Dissertation contains seven chapters, where the lead chapter deals with the background, history and introduction to bulk metallic glasses. The following four chapters are the published/to be published work, where the criterion for predicting glass formation, effect of Niobium addition on glass-forming ability (GFA), lattice contraction on

  3. Unveiling the complex electronic structure of amorphous metal oxides

    PubMed Central

    Århammar, C.; Pietzsch, Annette; Bock, Nicolas; Holmström, Erik; Araujo, C. Moyses; Gråsjö, Johan; Zhao, Shuxi; Green, Sara; Peery, T.; Hennies, Franz; Amerioun, Shahrad; Föhlisch, Alexander; Schlappa, Justine; Schmitt, Thorsten; Strocov, Vladimir N.; Niklasson, Gunnar A.; Wallace, Duane C.; Rubensson, Jan-Erik; Johansson, Börje; Ahuja, Rajeev

    2011-01-01

    Amorphous materials represent a large and important emerging area of material’s science. Amorphous oxides are key technological oxides in applications such as a gate dielectric in Complementary metal-oxide semiconductor devices and in Silicon-Oxide-Nitride-Oxide-Silicon and TANOS (TaN-Al2O3-Si3N4-SiO2-Silicon) flash memories. These technologies are required for the high packing density of today’s integrated circuits. Therefore the investigation of defect states in these structures is crucial. In this work we present X-ray synchrotron measurements, with an energy resolution which is about 5–10 times higher than is attainable with standard spectrometers, of amorphous alumina. We demonstrate that our experimental results are in agreement with calculated spectra of amorphous alumina which we have generated by stochastic quenching. This first principles method, which we have recently developed, is found to be superior to molecular dynamics in simulating the rapid gas to solid transition that takes place as this material is deposited for thin film applications. We detect and analyze in detail states in the band gap that originate from oxygen pairs. Similar states were previously found in amorphous alumina by other spectroscopic methods and were assigned to oxygen vacancies claimed to act mutually as electron and hole traps. The oxygen pairs which we probe in this work act as hole traps only and will influence the information retention in electronic devices. In amorphous silica oxygen pairs have already been found, thus they may be a feature which is characteristic also of other amorphous metal oxides.

  4. Morphological, structural, and spectral characteristics of amorphous iron sulfates

    NASA Astrophysics Data System (ADS)

    Sklute, E. C.; Jensen, H. B.; Rogers, A. D.; Reeder, R. J.

    2015-04-01

    Current or past brine hydrologic activity on Mars may provide suitable conditions for the formation of amorphous ferric sulfates. Once formed, these phases would likely be stable under current Martian conditions, particularly at low- to mid-latitudes. Therefore, we consider amorphous iron sulfates (AIS) as possible components of Martian surface materials. Laboratory AIS were created through multiple synthesis routes and characterized with total X-ray scattering, thermogravimetric analysis, scanning electron microscopy, visible/near-infrared (VNIR), thermal infrared (TIR), and Mössbauer techniques. We synthesized amorphous ferric sulfates (Fe(III)2(SO4)3 · ~ 6-8H2O) from sulfate-saturated fluids via vacuum dehydration or exposure to low relative humidity (<11%). Amorphous ferrous sulfate (Fe(II)SO4 · ~ 1H2O) was synthesized via vacuum dehydration of melanterite. All AIS lack structural order beyond 11 Å. The short-range (<5 Å) structural characteristics of amorphous ferric sulfates resemble all crystalline reference compounds; structural characteristics for the amorphous ferrous sulfate are similar to but distinct from both rozenite and szomolnokite. VNIR and TIR spectral data for all AIS display broad, muted features consistent with structural disorder and are spectrally distinct from all crystalline sulfates considered for comparison. Mössbauer spectra are also distinct from crystalline phase spectra available for comparison. AIS should be distinguishable from crystalline sulfates based on the position of their Fe-related absorptions in the visible range and their spectral characteristics in the TIR. In the NIR, bands associated with hydration at ~1.4 and 1.9 µm are significantly broadened, which greatly reduces their detectability in soil mixtures. AIS may contribute to the amorphous fraction of soils measured by the Curiosity rover.

  5. Relationship between amorphous silica and precious metal in quartz veins

    NASA Astrophysics Data System (ADS)

    Harrichhausen, N.; Rowe, C. D.; Board, W. S.; Greig, C. J.

    2015-12-01

    Super-saturation of silica is common in fault fluids, due to pressure changes associated with fracture, fault slip, or temperature gradients in hydrothermal systems. These mechanisms lead to precipitation of amorphous silica, which will recrystallize to quartz under typical geologic conditions. These conditions may also promote the saturation of precious metals, such as gold, and the precipitation of nanoparticles. Previous experiments show that charged nanoparticles of gold can attach to the surface of amorphous silica nanoparticles. Thus, gold and silica may be transported as a colloid influencing mineralization textures during amorphous silica recrystallization to quartz. This may enrich quartz vein hosted gold deposits, but the instability of hydrous silica during subsequent deformation means that the microstructural record of precipitation of gold is lost. We investigate a recent, shallow auriferous hydrothermal system at Dixie Valley, Nevada to reveal the nano- to micro-scale relationships between gold and silica in fresh veins. Fault slip surfaces at Dixie Valley exhibit layers of amorphous silica with partial recrystallization to quartz. Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) show amorphous silica can contain a few wt. % gold while areas recrystallized to quartz are barren. At the Jurassic Brucejack deposit in British Columbia, Canada we observe the cryptocrystalline quartz textures that may indicate recrystallization from amorphous silica within quartz-carbonate veins containing high grade gold. Comb quartz within syntaxial veins, vugs, and coating breccia clasts indicate structural dilation. Vein geometry is investigated to determine relative importance of fault slip in creating dilational sites. By comparing quartz-carbonate veins from the Dixie Valley to Brucejack, we can determine whether amorphous silica formed in different environments show similar potential to affect precious metal mineralization.

  6. Molecular mobility in amorphous state: Implications on physical stability

    NASA Astrophysics Data System (ADS)

    Bhardwaj, Sunny Piyush

    Amorphous pharmaceuticals are desirable in drug development due to their advantageous biopharmaceutical properties of higher apparent aqueous solubility and dissolution rate. The main obstacle in their widespread use, however, is their higher physicochemical instability than their crystalline counterparts. The goal of the present research project was to investigate correlations between the molecular mobility and physical stability in model amorphous compounds. The objective was to identify the specific mobility which is responsible for the physical instability in each case. This will potentially enable the development of effective strategies for the stabilization of amorphous pharmaceuticals. Moreover, these correlations can be used to develop predictive models for the stability at the pharmaceutically relevant storage conditions. Subtraction of dc conductivity enabled the comprehensive characterization of molecular mobility in amorphous trehalose. This was followed by investigation of correlation between crystallization behavior and different relaxations. Global mobility was found to be strongly coupled to both crystallization onset time and rate. Different preparation methods imparted different mobility states to amorphous trehalose which was postulated to be the reason for the significant physical stability differences. Predictive models were developed and a good agreement was found between the predicted and the experimental crystallization onset times at temperatures around and below the glass transition temperature (Tg). Effect of annealing was investigated on water sorption, enthalpic recovery and dielectric relaxation times in amorphous trehalose. Global mobility was found to be linearly correlated to the water sorption potential which enabled the development of predictive models. Global mobility was also found to be strongly correlated to physical instability in amorphous itraconazole. Effect of polymer (PVP and HPMCAS) on itraconazole mobility and

  7. Structural and Spectral Characteristics of Amorphous Iron Sulfates

    NASA Astrophysics Data System (ADS)

    Sklute, E.; Jensen, H. B.; Rogers, D.; Reeder, R. J.

    2014-12-01

    Substantial evidence points to the existence of hydrated sulfate phases on the Martian surface1-3. In addition, the discovery of recurring slope lineae could point to an active brine hydrologic cycle on the surface4,5. The rapid dehydration of both hydrated sulfates and sulfate-rich brines can lead to the formation of amorphous sulfates. Evidence suggests that the Rocknest soil target and the Sheepbed mudstone interrogated by the Mars Science Laboratory at Gale crater contain ~30 wt.% XRD amorphous material that is rich in both sulfur and iron6. These factors have led us to consider hydrated amorphous iron sulfates as possible components in Martian surface materials. Amorphous iron sulfates were created through multiple synthesis routes, and then characterized with total x-ray scattering, TGA, SEM, visible/near-infrared (VNIR), thermal infrared (TIR), and Mössbauer techniques. We synthesized amorphous ferric sulfates (Fe(III)2(SO4)3•~5-8H2O) from sulfate-saturated fluids via two pathways: vacuum dehydration and exposure to low relative humidity (<11%) using a LiCl buffer. Amorphous ferrous sulfate (Fe(II)SO4•~1H2O) was synthesized via vacuum dehydration of melanterite (Fe(II) SO4•7H2O). We find that both the ferric and ferrous sulfates synthesized from these methods lack long-range (>10Å) order, and thus are truly amorphous. VNIR and TIR spectral data for the amorphous sulfates display broad, muted features consistent with structural disorder and are spectrally distinct from all crystalline sulfates considered for comparison. Mössbauer spectra are also distinct from all crystalline phase spectra available for comparison. The amorphous sulfates should be distinguishable based on the position of their Fe-related absorptions in the visible range and their spectral characteristics in the TIR. In the NIR, which is the spectral range that has primarily been used to detect sulfates on Mars, the bands associated with hydration at ~1.4 and 1.9 μm are significantly

  8. Investigation of the Rigid Amorphous Fraction in Nylon-6

    SciTech Connect

    Chen,H.; Cebe, P.

    2007-01-01

    A three-phase model, comprising crystalline, mobile amorphous, and rigid amorphous fractions (X{sub c}, X{sub MA}, X{sub rA}, respectively) has been applied in the study of semicrystalline Nylon-6. The samples studied were Nylon-6 alpha phase prepared by subsequent annealing of a parent sample slowly cooled from the melt. The treated samples were annealed at 110 C, then briefly heated to 136 C, then re-annealed at 110 C. Temperature-modulated differential scanning calorimetry (TMDSC) measurements allow the devitrification of the rigid amorphous fraction to be examined. We observe a lower endotherm, termed the 'annealing' peak in the non-reversing heat flow after annealing at 110 C. By brief heating above this lower endotherm and immediately quenching in LN{sub 2}-cooled glass beads, the glass transition temperature and X{sub RA} decrease substantially, X{sub MA} increases, and the annealing peak disappears. The annealing peak corresponds to the point at which partial de-vitrification of the rigid amorphous fraction (RAF) occurs. Re-annealing at 110 C causes the glass transition and X{sub RA} to increase, and X{sub MA} to decrease. None of these treatments affected the measured degree of crystallinity, but it cannot be excluded that crystal reorganization or recrystallization may also occur at the annealing peak, contributing to the de-vitrification of the rigid amorphous fraction. Using a combined approach of thermal analysis with wide and small angle X-ray scattering, we analyze the location of the rigid amorphous and mobile amorphous fractions within the context of the Heterogeneous and Homogeneous Stack Models. Results show the homogeneous stack model is the correct one for Nylon-6. The cooperativity length ({var_epsilon}{sub A}) increases with a decrease of rigid amorphous fraction, or, increase of the mobile amorphous fraction. Devitrification of some of the RAF leads to the broadening of the glass transition region and shift of T{sub g}.

  9. Metastable Defects in Tritiated Amorphous Silicon

    SciTech Connect

    Ju, T.; Whitaker, J.; Zukotynski, S.; Kherani, N.; Taylor, P. C.; Stradins, P.

    2007-01-01

    The appearance of optically or electrically induced defects in hydrogenated amorphous silicon (a-Si:H), especially those that contribute to the Staebler-Wronski effect, has been the topic of numerous studies, yet the mechanism of defect creation and annealing is far from clarified. We have been observing the growth of defects caused by tritium decay in tritiated a Si-H instead of inducing defects optically. Tritium decays to {sup 3}He, emitting a beta particle (average energy of 5.7 keV) and an antineutrino. This reaction has a half-life of 12.5 years. In these 7 at.% tritium-doped a-Si:H samples each beta decay will create a defect by converting a bonded tritium to an interstitial helium, leaving behind a silicon dangling bond. We use ESR (electron spin resonance) and PDS( photothermal deflection spectroscopy) to track the defects. First we annealed these samples, and then we used ESR to determine the initial defect density around 10{sup 16} to 10{sup 17}/cm{sup 3}, which is mostly a surface spin density. After that we have kept the samples in liquid nitrogen for almost two years. During the two years we have used ESR to track the defect densities of the samples. The defect density increases without saturation to a value of 3 x 10{sup 19}/cm{sup 3} after two years, a number smaller than one would expect if each tritium decay were to create a silicon dangling bond (2 x 10{sup 20}/cm{sup 3}). This result suggests that there might be either an annealing process that remains at liquid nitrogen temperature, or tritium decay in clustered phase not producing a dangling bond due to bond reconstruction and emission of the hydrogen previously paired to Si-bonded tritium atom. After storage in liquid nitrogen for two years, we have annealed the samples. We have stepwise annealed one sample at temperatures up to 200, where all of the defects from beta decay are annealed out, and reconstructed the annealing energy distribution. The second sample, which was grown at 150, has

  10. Amorphization of hard crystalline materials by electrosprayed nanodroplet impact

    SciTech Connect

    Gamero-Castaño, Manuel Torrents, Anna; Borrajo-Pelaez, Rafael; Zheng, Jian-Guo

    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 transmission 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.

  11. Amorphous Li2 O2 : Chemical Synthesis and Electrochemical Properties.

    PubMed

    Zhang, Yelong; Cui, Qinghua; Zhang, Xinmin; McKee, William C; Xu, Ye; Ling, Shigang; Li, Hong; Zhong, Guiming; Yang, Yong; Peng, Zhangquan

    2016-08-26

    When aprotic Li-O2 batteries discharge, the product phase formed in the cathode often contains two different morphologies, that is, crystalline and amorphous Li2 O2 . The morphology of Li2 O2 impacts strongly on the electrochemical performance of Li-O2 cells in terms of energy efficiency and rate capability. Crystalline Li2 O2 is readily available and its properties have been studied in depth for Li-O2 batteries. However, little is known about the amorphous Li2 O2 because of its rarity in high purity. Herein, amorphous Li2 O2 has been synthesized by a rapid reaction of tetramethylammonium superoxide and LiClO4 in solution, and its amorphous nature has been confirmed by a range of techniques. Compared with its crystalline siblings, amorphous Li2 O2 demonstrates enhanced charge-transport properties and increased electro-oxidation kinetics, manifesting itself a desirable discharge phase for high-performance Li-O2 batteries. PMID:27486085

  12. Shock consolidation of mechanically alloyed amorphous Ti-Si powders

    SciTech Connect

    Glade, S.C.; Thadhani, N.N.

    1995-10-01

    Mechanical alloying was used to synthesize amorphous 5Ti-3Si atomic ratio powders in a SPEX mill under Ar atmosphere. X-ray diffraction analysis revealed formation of a single-phase amorphous compound after about 24 hours of milling. High-resolution transmission electron microscopy (TEM) showed that the milled powder still contained nanocrystallites of Ti and Si among regions of generally amorphous compound. The mechanically alloyed amorphous powder was shock consolidated, using a plate impact assembly, to produce bulk compacts. The compaction resulted in a significant amount of crystallization, forming 30- to 40-nm crystals of TiSi{sub 2} and Ti{sub 5}Si{sub 3} intermetallic compounds. The compacts were subsequently annealed above the crystallization temperature, measured to be {approximately}640 C using differential thermal analysis. The compacts annealed at 800 C for 1 hour showed only limited grain growth to {approximately}50-nm crystallite size. Microhardness of the shocked amorphous alloy compacts was {approximately}1,100 KHN, which increased to {approximately}1,250 KHN upon subsequent annealing, with the formation of a more homogeneous nanocrystalline microstructure.

  13. Amorphous and Nanocomposite Materials for Energy-Efficient Electric Motors

    NASA Astrophysics Data System (ADS)

    Silveyra, Josefina M.; Xu, Patricia; Keylin, Vladimir; DeGeorge, Vincent; Leary, Alex; McHenry, Michael E.

    2016-01-01

    We explore amorphous soft-magnetic alloys as candidates for electric motor applications. The Co-rich system combines the benefits of low hysteretic and eddy-current losses while exhibiting negligible magnetostriction and robust mechanical properties. The amorphous precursors can be devitrified to form nanocomposite magnets. The superior characteristics of these materials offer the advantages of ease of handling in the manufacturing processing and low iron losses during motor operation. Co-rich amorphous ribbons were laser-cut to build a stator for a small demonstrator permanent-magnet machine. The motor was tested up to ~30,000 rpm. Finite-element analyses proved that the iron losses of the Co-rich amorphous stator were ~80% smaller than for a Si steel stator in the same motor, at 18,000 rpm (equivalent to an electric frequency of 2.1 kHz). These low-loss soft magnets have great potential for application in highly efficient high-speed electric machines, leading to size reduction as well as reduction or replacement of rare earths in permanent-magnet motors. More studies evaluating further processing techniques for amorphous and nanocomposite materials are needed.

  14. Amorphous computing in the presence of stochastic disturbances.

    PubMed

    Chu, Dominique; Barnes, David J; Perkins, Samuel

    2014-11-01

    Amorphous computing is a non-standard computing paradigm that relies on massively parallel execution of computer code by a large number of small, spatially distributed, weakly interacting processing units. Over the last decade or so, amorphous computing has attracted a great deal of interest both as an alternative model of computing and as an inspiration to understand developmental biology. A number of algorithms have been developed that can take advantage of the massive parallelism of this computing paradigm to solve specific problems. One of the interesting properties of amorphous computers is that they are robust with respect to the loss of individual processing units, in the sense that a removal of some of them should not impact on the computation as a whole. However, much less understood is to what extent amorphous computers are robust with respect to minor disturbances to the individual processing units, such as random motion or occasional faulty computation short of total component failure. In this article we address this question. As an example problem we choose an algorithm to calculate a straight line between two points. Using this example, we find that amorphous computers are not in general robust with respect to Brownian motion and noise, but we find strategies that restore reliable computation even in their presence. We will argue that these strategies are generally applicable and not specific to the particular AC we consider, or even specific to electronic computers.

  15. Parametrized dielectric functions of amorphous GeSn alloys

    SciTech Connect

    D'Costa, Vijay Richard Wang, Wei; Yeo, Yee-Chia; Schmidt, Daniel

    2015-09-28

    We obtained the complex dielectric function of amorphous Ge{sub 1−x}Sn{sub x} (0 ≤ x ≤ 0.07) alloys using spectroscopic ellipsometry from 0.4 to 4.5 eV. Amorphous GeSn films were formed by room-temperature implantation of phosphorus into crystalline GeSn alloys grown by molecular beam epitaxy. The optical response of amorphous GeSn alloys is similar to amorphous Ge and can be parametrized using a Kramers-Kronig consistent Cody-Lorentz dispersion model. The parametric model was extended to account for the dielectric functions of amorphous Ge{sub 0.75}Sn{sub 0.25} and Ge{sub 0.50}Sn{sub 0.50} alloys from literature. The compositional dependence of band gap energy E{sub g} and parameters associated with the Lorentzian oscillator have been determined. The behavior of these parameters with varying x can be understood in terms of the alloying effect of Sn on Ge.

  16. Amorphous metal distribution transformers: The energy-efficient alternative

    SciTech Connect

    Garrity, T.F.

    1994-12-31

    Amorphous metal distribution transformers have been commercially available for the past 13 years. During that time, they have realized the promise of exceptionally high core efficiency as compared to silicon steel transformer cores. Utility planners today must consider all options available to meet the requirements of load growth. While additional generation capacity will be added, many demand-side initiatives are being undertaken as complementary programs to generation expansion. The efficiency improvement provided by amorphous metal distribution transformers deserves to be among the demand-side options. The key to understanding the positive impact of amorphous metal transformer efficiency is to consider the aggregate contribution those transformers can make towards demand reduction. It is estimated that distribution transformer core losses comprise at least 1% of the utility`s peak demand. Because core losses are continuous, any significant reduction in their magnitude is of great significance to the planner. This paper describes the system-wide economic contributions amorphous metal distribution transformers can make to a utility and suggests evaluation techniques that can be used. As a conservation tool, the amorphous metal transformer contributes to reduced power plant emissions. Calibration of those emissions reductions is also discussed in the paper.

  17. Infrared Spectra and Optical Constants of Elusive Amorphous Methane

    NASA Technical Reports Server (NTRS)

    Gerakines, Perry A.; Hudson, Reggie L.

    2015-01-01

    New and accurate laboratory results are reported for amorphous methane (CH4) ice near 10 K for the study of the interstellar medium (ISM) and the outer Solar System. Near- and mid-infrared (IR) data, including spectra, band strengths, absorption coefficients, and optical constants, are presented for the first time for this seldom-studied amorphous solid. The apparent IR band strength near 1300 cm(exp -1) (7.69 micrometer) for amorphous CH4 is found to be about 33% higher than the value long used by IR astronomers to convert spectral observations of interstellar CH4 into CH4 abundances. Although CH4 is most likely to be found in an amorphous phase in the ISM, a comparison of results from various laboratory groups shows that the earlier CH4 band strength at 1300 cm(exp -1) (7.69 micrometer) was derived from IR spectra of ices that were either partially or entirely crystalline CH4 Applications of the new amorphous-CH4 results are discussed, and all optical constants are made available in electronic form.

  18. Crystallization of amorphous water ice in the solar system

    NASA Technical Reports Server (NTRS)

    Jenniskens, P.; Blake, D. F.

    1996-01-01

    Electron diffraction studies of vapor-deposited water ice have characterized the dynamical structural changes during crystallization that affect volatile retention in cometary materials. Crystallization is found to occur by nucleation of small domains, while leaving a significant part of the amorphous material in a slightly more relaxed amorphous state that coexists metastably with cubic crystalline ice. The onset of the amorphous relaxation is prior to crystallization and coincides with the glass transition. Above the glass transition temperature, the crystallization kinetics are consistent with the amorphous solid becoming a "strong" viscous liquid. The amorphous component can effectively retain volatiles during crystallization if the volatile concentration is approximately 10% or less. For higher initial impurity concentrations, a significant amount of impurities is released during crystallization, probably because the impurities are trapped on the surfaces of micropores. A model for crystallization over long timescales is described that can be applied to a wide range of impure water ices under typical astrophysical conditions if the fragility factor D, which describes the viscosity behavior, can be estimated.

  19. Self-organization of a periodic structure between amorphous and crystalline phases in a GeTe thin film induced by femtosecond laser pulse amorphization

    SciTech Connect

    Katsumata, Y.; Morita, T.; Morimoto, Y.; Shintani, T.; Saiki, T.

    2014-07-21

    A self-organized fringe pattern in a single amorphous mark of a GeTe thin film was formed by multiple femtosecond pulse amorphization. Micro Raman measurement indicates that the fringe is a periodic alternation between crystalline and amorphous phases. The period of the fringe is smaller than the irradiation wavelength and the direction is parallel to the polarization direction. Snapshot observation revealed that the fringe pattern manifests itself via a complex but coherent process, which is attributed to crystallization properties unique to a nonthermally amorphized phase and the distinct optical contrast between crystalline and amorphous phases.

  20. Amorphous AlPO sub 4 as catalyst support: 2. Characterization of amorphous aluminum phosphates

    SciTech Connect

    Rebenstorf, B.; Lindblad, T.; Andersson, S.L.T. )

    1991-04-01

    Three different amorphous aluminum phosphates have been characterized by their specific surface area and pore volume and by XPS and FTIR studies. Three types of Al surface hydroxyl groups at 3793.8, 3768.5, and 3743.2 cm{sup {minus}1} and only one type of P surface hydroxyl groups at 3677.5 cm{sup {minus}1} are found in FTIR spectra after evacuation at 800{degree}C. The ratio of the integrated absorbance of the IR bands from AlOH and POH surface groups is a sensitive tool to study the surface of AlPO{sub 4} directly. A linear relation between the electronegativity of the metal ion and the stretching vibration of surface hydroxyl groups is proposed for Al, Si, P, and B tetrahedral surface ions. The three Al surface hydroxyl groups are assigned to four-coordinated (tetrahedral), five-coordinated, and six-coordinated surface Al ions. Amorphous AlPO{sub 4} contains four- and five-coordinated Al ions and AlPO{sub 4} with high specific surface area also has six-coordinated Al ions at the surface. CO is adsorbed on the phosphorus surface hydroxyl groups at low temperature, giving an IR band at 2170 cm{sup {minus}1}, while the IR band from the PO-H group is shifted to 3495 cm{sup {minus}1}. On AlPO{sub 4} of high surface area, CO is also adsorbed on coordinatively unsaturated, five-coordinated Al surface ions. Four-coordinated Al ions are also found, but none with the coordination number three. Impregnation with chromium compounds in ethanol does not change the specific surface area, whereas impregnation in water resulted in a decreased specific surface area, to less than half of its previous value.

  1. Matrix sublimation method for the formation of high-density amorphous ice

    NASA Astrophysics Data System (ADS)

    Kouchi, A.; Hama, T.; Kimura, Y.; Hidaka, H.; Escribano, R.; Watanabe, N.

    2016-08-01

    A novel method for the formation of amorphous ice involving matrix sublimation has been developed. A CO-rich CO:H2O mixed ice was deposited at 8-10 K under ultra-high vacuum condition, which was then allowed to warm. After the sublimation of matrix CO at 35 K, amorphous ice remained. The amorphous ice formed exhibits a highly porous microscale texture; however, it also rather exhibits a density similar to that of high-density amorphous ice formed under high pressure. Furthermore, unlike conventional vapor-deposited amorphous ice, the amorphous ice is stable up to 140 K, where it transforms directly to cubic ice Ic.

  2. Connecting Local Yield Stresses with Plastic Activity in Amorphous Solids

    NASA Astrophysics Data System (ADS)

    Patinet, Sylvain; Vandembroucq, Damien; Falk, Michael L.

    2016-07-01

    In model amorphous solids produced via differing quench protocols, a strong correlation is established between local yield stress measured by direct local probing of shear stress thresholds and the plastic rearrangements observed during remote loading in shear. This purely local measure shows a higher predictive power for identifying sites of plastic activity when compared with more conventional structural properties. Most importantly, the sites of low local yield stress, thus defined, are shown to be persistent, remaining predictive of deformation events even after fifty or more such plastic rearrangements. This direct and nonperturbative approach gives access to relevant transition pathways that control the stability of amorphous solids. Our results reinforce the relevance of modeling plasticity in amorphous solids based on a gradually evolving population of discrete and local zones preexisting in the structure.

  3. Connecting Local Yield Stresses with Plastic Activity in Amorphous Solids.

    PubMed

    Patinet, Sylvain; Vandembroucq, Damien; Falk, Michael L

    2016-07-22

    In model amorphous solids produced via differing quench protocols, a strong correlation is established between local yield stress measured by direct local probing of shear stress thresholds and the plastic rearrangements observed during remote loading in shear. This purely local measure shows a higher predictive power for identifying sites of plastic activity when compared with more conventional structural properties. Most importantly, the sites of low local yield stress, thus defined, are shown to be persistent, remaining predictive of deformation events even after fifty or more such plastic rearrangements. This direct and nonperturbative approach gives access to relevant transition pathways that control the stability of amorphous solids. Our results reinforce the relevance of modeling plasticity in amorphous solids based on a gradually evolving population of discrete and local zones preexisting in the structure. PMID:27494480

  4. Amorphous intergranular phases control the properties of rodent tooth enamel

    NASA Astrophysics Data System (ADS)

    Gordon, Lyle M.; Cohen, Michael J.; MacRenaris, Keith W.; Pasteris, Jill D.; Seda, Takele; Joester, Derk

    2015-02-01

    Dental enamel, a hierarchical material composed primarily of hydroxylapatite nanowires, is susceptible to degradation by plaque biofilm-derived acids. The solubility of enamel strongly depends on the presence of Mg2+, F-, and CO32-. However, determining the distribution of these minor ions is challenging. We show—using atom probe tomography, x-ray absorption spectroscopy, and correlative techniques—that in unpigmented rodent enamel, Mg2+ is predominantly present at grain boundaries as an intergranular phase of Mg-substituted amorphous calcium phosphate (Mg-ACP). In the pigmented enamel, a mixture of ferrihydrite and amorphous iron-calcium phosphate replaces the more soluble Mg-ACP, rendering it both harder and more resistant to acid attack. These results demonstrate the presence of enduring amorphous phases with a dramatic influence on the physical and chemical properties of the mature mineralized tissue.

  5. Amorphous copper tungsten oxide with tunable band gaps

    SciTech Connect

    Chen Le; Shet, Sudhakar; Tang Houwen; Wang Heli; Yan Yanfa; Turner, John; Al-Jassim, Mowafak; Ahn, Kwang-soon

    2010-08-15

    We report on the synthesis of amorphous copper tungsten oxide thin films with tunable band gaps. The thin films are synthesized by the magnetron cosputtering method. We find that due to the amorphous nature, the Cu-to-W ratio in the films can be varied without the limit of the solubility (or phase separation) under appropriate conditions. As a result, the band gap and conductivity type of the films can be tuned by controlling the film composition. Unfortunately, the amorphous copper tungsten oxides are not stable in aqueous solution and are not suitable for the application of photoelectrochemical splitting of water. Nonetheless, it provides an alternative approach to search for transition metal oxides with tunable band gaps.

  6. Phase diagrams of a ferromagnetic amorphous bilayer system

    NASA Astrophysics Data System (ADS)

    Bengrine, M.; Benyoussef, A.; El Kenz, A.; Loulidi, M.; Mhirech, F.

    1998-03-01

    Using the effective-field theory, we study phase diagrams of a ferromagnetic amorphous bilayer system, consisting of two monolayers (A and B) with different spins ( SA= {1}/{2} and SB= {1}/{2}, 1) and different interaction constants coupled together with an interlayer coupling. The effects of amorphization in the monolayer B and in the interlayer coupling are investigated. The influence of the crystal-field interaction D, in the case SA= {1}/{2} and SB=1, is also studied. A number of interesting phenomena are obtained such as the dependence of the tricritical behavior on amorphization. Other phenomena have been given in a variety of phase diagrams. The temperature dependence of the total magnetization is also examined.

  7. Connecting Local Yield Stresses with Plastic Activity in Amorphous Solids.

    PubMed

    Patinet, Sylvain; Vandembroucq, Damien; Falk, Michael L

    2016-07-22

    In model amorphous solids produced via differing quench protocols, a strong correlation is established between local yield stress measured by direct local probing of shear stress thresholds and the plastic rearrangements observed during remote loading in shear. This purely local measure shows a higher predictive power for identifying sites of plastic activity when compared with more conventional structural properties. Most importantly, the sites of low local yield stress, thus defined, are shown to be persistent, remaining predictive of deformation events even after fifty or more such plastic rearrangements. This direct and nonperturbative approach gives access to relevant transition pathways that control the stability of amorphous solids. Our results reinforce the relevance of modeling plasticity in amorphous solids based on a gradually evolving population of discrete and local zones preexisting in the structure.

  8. Substrate/layer interface of amorphous-carbon hard coatings

    NASA Astrophysics Data System (ADS)

    Böhme, O.; Cebollada, A.; Yang, S.; Teer, D. G.; Albella, J. M.; Román, E.

    2000-08-01

    A combined study of the crystalline structure, the chemical interaction, and diffusion processes of the substrate/layer interface of amorphous-carbon hard coatings is presented. The structure of the coatings and their gradient layer interface to a chromium buffer layer has been investigated on two substrates [Si(100) and tool steel] using x-ray diffraction (XRD). Chemical interaction and diffusion processes at the interfaces and within the layers were analyzed by Auger electron spectroscopy and x-ray photoemission spectroscopy depth profiles. The chromium buffer layer revealed similar textured structure on both substrates. The subsequent gradient layer was determined (within XRD limits) to be amorphous and composed of an amorphous-carbon and chromium-carbide composite. The chromium carbide maintains the same stoichiometry (Cr3C2), regardless of the gradually changing chromium content. No large-scale interdiffusion was measured, either between or within the layers.

  9. International Ultraviolet Explorer observations of amorphous hot galaxies

    SciTech Connect

    Lamb, S.A.; Gallagher, J.S. III; Hjellming, M.S.; Hunter, D.A.

    1984-08-01

    In order to better understand the nature of star formation processes in amorphous galaxies, short wavelength International Ultraviolet Explorer (IUE) spectra of galaxies NGC 1705 and NGC 1800 were obtained. The IUE data for NGC 1705 were of excellent quality while the low signal-to-noise NGC 1800 observation was useful only as a rough guide to the ultraviolet energy distribution. It was found that NGC 1705 contains a normal mix of OB stars, which is consistent with the nearly constant recent star formation rate inferred from new optical data. The NGC 1800 is likely to have similar properties, and blue galaxies with amorphous structures thus do not show evidence for anomalies in stellar mass distributions. The UV spectra of amorphous galaxies and a variety of other hot extragalactic stellar systems have similar characteristics, which suggests OB stellar populations often are homogeneous in their properties.

  10. Electrooptical properties and structural features of amorphous ITO

    SciTech Connect

    Amosova, L. P.

    2015-03-15

    Thin indium-tin oxide (ITO) films are deposited onto cold substrates by magnetron-assisted sputtering. The dependences of the structural, electrical, and optical properties of the films on the oxygen content in the atmosphere of sputtering and the growth rate are studied. It is shown that, if the substrate temperature is no higher than the ITO crystallization temperature and the conditions of growth deviate from the optimal relationship between the oxygen pressure and the growth rate, the resistance of the layers can be six or seven orders of magnitude higher than the resistance of conducting amorphous layers and reach hundreds of megaohms. At the same time, the optical properties of insulating layers in the visible spectral region are completely identical to the properties of the conducing amorphous modification. A conceptual model of defects responsible for the insulating properties of amorphous ITO is proposed.

  11. International Ultraviolet Explorer observations of amorphous hot galaxies

    NASA Technical Reports Server (NTRS)

    Lamb, S. A.; Gallac gher, J. S.; Hjellming, M.; Hunter, D. A.

    1984-01-01

    In order to better understand the nature of star formation processes in amorphous galaxies, short wavelength International Ultraviolet Explorer (IUE) spectra of galaxies NGC 1705 and NGC 1800 were obtained. The IUE data for NGC 1705 were of excellent quality while the low signal-to-noise NGC 1800 observation was useful only as a rough guide to the ultraviolet energy distribution. It was found that NGC 1705 contains a normal mix of OB stars, which is consistent with the nearly constant recent star formation rate inferred from new optical data. The NGC 1800 is likely to have similar properties, and blue galaxies with amorphous structures thus do not show evidence for anomalies in stellar mass distributions. The UV spectra of amorphous galaxies and a variety of other hot extragalactic stellar systems have similar characteristics, which suggests OB stellar populations often are homogeneous in their properties.

  12. Flexible Protocrystalline Silicon Solar Cells with Amorphous Buffer Layer

    NASA Astrophysics Data System (ADS)

    Ishikawa, Yasuaki; Schubert, Markus B.

    2006-09-01

    A low deposition temperature of 110 °C is mandatory for directly growing amorphous-silicon-based solar cells on plastic foil. The optimum absorber material at this low temperature is protocrystalline, i.e., right at the transition between amorphous and crystalline silicon. Polyethylene terephtalate foil of 50 μm thickness form the substrate of our flexible p-i-n single-junction cells. We discuss three peculiar processing techniques for achieving the maximum photovoltaic conversion efficiency of flexible low-temperature solar cells. First, we employ an optimized microcrystalline silicon p-type window layer; second, we use protocrystalline silicon for the i-layer; third, we insert an undoped amorphous silicon buffer layer at the p/i interface. The best flexible cells attain power conversion efficiencies of up to 4.9%.

  13. Amorphous Alloy Membranes for High Temperature Hydrogen Separation

    SciTech Connect

    Coulter, K

    2013-09-30

    At the beginning of this project, thin film amorphous alloy membranes were considered a nascent but promising new technology for industrial-scale hydrogen gas separations from coal- derived syngas. This project used a combination of theoretical modeling, advanced physical vapor deposition fabricating, and laboratory and gasifier testing to develop amorphous alloy membranes that had the potential to meet Department of Energy (DOE) targets in the testing strategies outlined in the NETL Membrane Test Protocol. The project is complete with Southwest Research Institute® (SwRI®), Georgia Institute of Technology (GT), and Western Research Institute (WRI) having all operated independently and concurrently. GT studied the hydrogen transport properties of several amorphous alloys and found that ZrCu and ZrCuTi were the most promising candidates. GT also evaluated the hydrogen transport properties of V, Nb and Ta membranes coated with different transition-metal carbides (TMCs) (TM = Ti, Hf, Zr) catalytic layers by employing first-principles calculations together with statistical mechanics methods and determined that TiC was the most promising material to provide catalytic hydrogen dissociation. SwRI developed magnetron coating techniques to deposit a range of amorphous alloys onto both porous discs and tubular substrates. Unfortunately none of the amorphous alloys could be deposited without pinhole defects that undermined the selectivity of the membranes. WRI tested the thermal properties of the ZrCu and ZrNi alloys and found that under reducing environments the upper temperature limit of operation without recrystallization is ~250 °C. There were four publications generated from this project with two additional manuscripts in progress and six presentations were made at national and international technical conferences. The combination of the pinhole defects and the lack of high temperature stability make the theoretically identified most promising candidate amorphous alloys

  14. Orientational disorder: A mechanism of amorphization at high pressure

    NASA Astrophysics Data System (ADS)

    Sakuntala, T.; Arora, A. K.; Shekar, N. V. Chandra; Sahu, P. Ch.

    1998-12-01

    Amorphization generally arises due to chemical disorder, high defect density or kinetic hindrances of equilibrium phase transitions. In this paper, we report that it can also be driven by orientational disorder of polyatomic ions or units. In potash alum, some of the sulphate ions are misoriented with their S-O bonds pointing towards potassium rather than towards aluminum, leading to an "orientational disorder" which ranges from 10 to 24%. Raman spectroscopic and X-ray diffraction studies reveal that samples with high initial orientational disorder exhibit a "reversible" amorphization at pressure around 60 kbar whereas those with low initial disorder exhibit an "irreversible" structural transition to a disorder-free crystalline phase.

  15. Single atom catalysts on amorphous supports: A quenched disorder perspective

    SciTech Connect

    Peters, Baron; Scott, Susannah L.

    2015-03-14

    Phenomenological models that invoke catalyst sites with different adsorption constants and rate constants are well-established, but computational and experimental methods are just beginning to provide atomically resolved details about amorphous surfaces and their active sites. This letter develops a statistical transformation from the quenched disorder distribution of site structures to the distribution of activation energies for sites on amorphous supports. We show that the overall kinetics are highly sensitive to the precise nature of the low energy tail in the activation energy distribution. Our analysis motivates further development of systematic methods to identify and understand the most reactive members of the active site distribution.

  16. Shape anisotropy in zero-magnetostrictive rapidly solidified amorphous nanowires

    NASA Astrophysics Data System (ADS)

    Rotărescu, C.; Atitoaie, A.; Stoleriu, L.; Óvári, T.-A.; Lupu, N.; Chiriac, H.

    2016-04-01

    The magnetic behavior of zero-magnetostrictive rapidly solidified amorphous nanowires has been investigated in order to understand their magnetic bistability. The study has been performed both experimentally - based on inductive hysteresis loop measurements - and theoretically, by means of micromagnetic simulations. Experimental hysteresis loops have shown that the amorphous nanowires display an axial magnetic bistability, characterized by a single-step magnetization reversal when the applied field reaches a critical value called switching field. The simulated loops allowed us to understand the effect of shape anisotropy on coercivity. The results are key for understanding and controlling the magnetization processes in these novel nanowires, with important application possibilities in new miniaturized sensing devices.

  17. Amorphous Zr-Based Foams with Aligned, Elongated Pores

    NASA Astrophysics Data System (ADS)

    Cox, Marie E.; Mathaudhu, Suveen N.; Hartwig, K. Ted; Dunand, David C.

    2010-07-01

    Interpenetrating phase composites are created by warm equal channel angular extrusion (ECAE) of blended powders of amorphous Zr58.5Nb2.8Cu15.6Ni12.8Al10.3 (Vit106a) and a crystalline ductile metal (Cu, Ni, or W). Subsequent dissolution of the continuous metallic phase results in amorphous Vit106a foams with ~40 pct aligned, elongated pores. The extent of Vit106a powder densification in the composites improves with the strength of the crystalline metallic powder, from low for Cu to high for W, with a concomitant improvement in foam compressive strength, ductility, and energy absorption.

  18. Polyamorphism in Water: Amorphous Ices and their Glassy States

    NASA Astrophysics Data System (ADS)

    Amann-Winkel, K.; Boehmer, R.; Fujara, F.; Gainaru, C.; Geil, B.; Loerting, T.

    2015-12-01

    Water is ubiquitous and of general importance for our environment. But it is also known as the most anomalous liquid. The fundamental origin of the numerous anomalies of water is still under debate. An understanding of these anomalous properties of water is closely linked to an understanding of the phase diagram of the metastable non-crystalline states of ice. The process of pressure induced amorphization of ice was first observed by Mishima et al. [1]. The authors pressurized hexagonal ice at 77 K up to a pressure of 1.6 GPa to form high density amorphous ice (HDA). So far three distinct structural states of amorphous water are known [2], they are called low- (LDA), high- (HDA) and very high density amorphous ice (VHDA). Since the discovery of multiple distinct amorphous states it is controversy discussed whether this phenomenon of polyamorphism at high pressures is connected to the occurrence of more than one supercooled liquid phase [3]. Alternatively, amorphous ices have been suggested to be of nanocrystalline nature, unrelated to liquids. Indeed inelastic X-ray scattering measurements indicate sharp crystal-like phonons in the amorphous ices [4]. In case of LDA the connection to the low-density liquid (LDL) was inferred from several experiments including the observation of a calorimetric glass-to-liquid transition at 136 K and ambient pressure [5]. Recently also the glass transition in HDA was observed at 116 K at ambient pressure [6] and at 140 K at elevated pressure of 1 GPa [7], using calorimetric measurements as well as dielectric spectroscopy. We discuss here the general importance of amorphous ices and their liquid counterparts and present calorimetric and dielectric measurements on LDA and HDA. The good agreement between dielectric and calorimetric results convey for a clearer picture of water's vitrification phenomenon. [1] O. Mishima, L. D. Calvert, and E. Whalley, Nature 314, 76, 1985 [2] D.T. Bowron, J. L. Finney, A. Hallbrucker, et al., J. Chem

  19. Embrittlement of Metal by Solute Segregation-Induced Amorphization

    SciTech Connect

    Chen, H.-P.; Kalia, Rajiv K.; Nakano, Aiichiro; Nomura, Ken-ichi; Vashishta, Priya; Yuan, Zaoshi; Kaxiras, Efthimios; Lu, Gang; Duin, Adri C. T. van

    2010-04-16

    Impurities segregated to grain boundaries of a material essentially alter its fracture behavior. A prime example is sulfur segregation-induced embrittlement of nickel, where an observed relation between sulfur-induced amorphization of grain boundaries and embrittlement remains unexplained. Here, 48x10{sup 6}-atom reactive-force-field molecular dynamics simulations provide the missing link. Namely, an order-of-magnitude reduction of grain-boundary shear strength due to amorphization, combined with tensile-strength reduction, allows the crack tip to always find an easy propagation path.

  20. Containerless synthesis of amorphous and nanophase organic materials

    DOEpatents

    Benmore, Chris J.; Weber, Johann R.

    2016-05-03

    The invention provides a method for producing a mixture of amorphous compounds, the method comprising supplying a solution containing the compounds; and allowing at least a portion of the solvent of the solution to evaporate while preventing the solute of the solution from contacting a nucleation point. Also provided is a method for transforming solids to amorphous material, the method comprising heating the solids in an environment to form a melt, wherein the environment contains no nucleation points; and cooling the melt in the environment.

  1. Directional amorphization of boron carbide subjected to laser shock compression

    DOE PAGES

    Zhao, Shiteng; Kad, Bimal; Remington, Bruce A.; LaSalvia, Jerry C.; Wehrenberg, Christopher E.; Behler, Kristopher D.; Meyers, Marc A.

    2016-10-12

    When crystalline solids are stressed quasi-statically, dislocation slip, twinning, and phase transformations are the predominant mechanisms to dissipate the imparted elastic energy. Under shock, high hydrostatic and shear stresses promptly build up at the shock front, favoring fast energy dissipation mechanisms. Amorphization, which may only involve localized atomic arrangements, is therefore an additional potential candidate. Shock-induced amorphization has now been reported in various materials and hence should be incorporated as a deformation/damage mechanism of crystals subjected to high-strain-rate loading.

  2. A transparent ultraviolet triggered amorphous selenium p-n junction

    SciTech Connect

    Saito, Ichitaro; Soga, Kenichi; Overend, Mauro; Amaratunga, Gehan A. J.; Miyazaki, Wataru; Onishi, Masanori; Masuzawa, Tomoaki; Okano, Ken; Kudo, Yuki; Yamada, Takatoshi; Koh, Angel; Chua, Daniel; Aono, Masami

    2011-04-11

    This paper will introduce a semitransparent amorphous selenium (a-Se) film exhibiting photovoltaic effects under ultraviolet light created through a simple and inexpensive method. We found that chlorine can be doped into a-Se through electrolysis of saturated salt water, and converts the weak p-type material into an n-type material. Furthermore, we found that a p-n diode fabricated through this process has shown an open circuit voltage of 0.35 V toward ultraviolet illumination. Our results suggest the possibility of doping control depending on the electric current during electrolysis and the possibility of developing a simple doping method for amorphous photoconductors.

  3. Shock-induced localized amorphization in boron carbide.

    PubMed

    Chen, Mingwei; McCauley, James W; Hemker, Kevin J

    2003-03-01

    High-resolution electron microscope observations of shock-loaded boron carbide have revealed the formation of nanoscale intragranular amorphous bands that occur parallel to specific crystallographic planes and contiguously with apparent cleaved fracture surfaces. This damage mechanism explains the measured, but not previously understood, decrease in the ballistic performance of boron carbide at high impact rates and pressures. The formation of these amorphous bands is also an example of how shock loading can result in the synthesis of novel structures and materials with substantially altered properties.

  4. Transmissive metallic contact for amorphous silicon solar cells

    DOEpatents

    Madan, A.

    1984-11-29

    A transmissive metallic contact for amorphous silicon semiconductors includes a thin layer of metal, such as aluminum or other low work function metal, coated on the amorphous silicon with an antireflective layer coated on the metal. A transparent substrate, such as glass, is positioned on the light reflective layer. The metallic layer is preferably thin enough to transmit at least 50% of light incident thereon, yet thick enough to conduct electricity. The antireflection layer is preferably a transparent material that has a refractive index in the range of 1.8 to 2.2 and is approximately 550A to 600A thick.

  5. Clathrate hydrate formation in amorphous cometary ice analogs in vacuo

    NASA Technical Reports Server (NTRS)

    Blake, David; Allamandola, Louis; Sandford, Scott; Hudgins, Doug; Freund, Friedemann

    1991-01-01

    Experiments conducted in clathrate hydrates with a modified electron microscope have demonstrated the possibility of such compounds' formation during the warming of vapor-deposited amorphous ices in vacuo, through rearrangements in the solid state. Subsolidus crystallization of compositionally complex amorphous ices may therefore be a general and ubiquitous process. Phase separations and microporous textures thus formed may be able to account for such anomalous cometary phenomena as the release of gas at large radial distances from the sun and the retention of volatiles to elevated temperatures.

  6. Magnetostriction behavior of Co-Fe-Si-B amorphous alloys

    SciTech Connect

    Gomez-Polo, C.; Pulido, E. ); Rivero, G.; Hernando, A. )

    1990-05-01

    It is well known that the saturation magnetostriction constant of nearly-zero-magnetostriction amorphous alloys exhibits a dependence on both magnetic field and applied stress. Therefore the anisotropy field induced by the applied stress does not depend linearly on the stress strength. Experiments carried out on Co-rich amorphous alloys show a stress dependence of the anisotropy field as that expected by assuming long-range fluctuations of the magnetoelastic anisotropy. In this report the existence of local fluctuations of saturation magnetostriction is shown to be a reasonable cause of the stress dependence of magnetostriction.

  7. Light-induced metastable structural changes in hydrogenated amorphous silicon

    SciTech Connect

    Fritzsche, H.

    1996-09-01

    Light-induced defects (LID) in hydrogenated amorphous silicon (a-Si:H) and its alloys limit the ultimate efficiency of solar panels made with these materials. This paper reviews a variety of attempts to find the origin of and to eliminate the processes that give rise to LIDs. These attempts include novel deposition processes and the reduction of impurities. Material improvements achieved over the past decade are associated more with the material`s microstructure than with eliminating LIDs. We conclude that metastable LIDs are a natural by-product of structural changes which are generally associated with non-radiative electron-hole recombination in amorphous semiconductors.

  8. Electrical characteristics of amorphous iron-tungsten contacts on silicon

    NASA Technical Reports Server (NTRS)

    Finetti, M.; Pan, E. T.-S.; Nicolet, M.-A.; Suni, I.

    1983-01-01

    The electrical characteristics of amorphous Fe-W contacts have been determined on both p-type and n-type silicon. The amorphous films were obtained by cosputtering from a composite target. Contact resistivities of 1 x 10 to the -7th and 2.8 x 10 to the -6th were measured on n(+) and p(+) silicon, respectively. These values remain constant after thermal treatment up to at least 500 C. A barrier height of 0.61 V was measured on n-type silicon.

  9. Amorphous calcium phosphate is a major component of the forming fin bones of zebrafish: Indications for an amorphous precursor phase.

    PubMed

    Mahamid, Julia; Sharir, Amnon; Addadi, Lia; Weiner, Steve

    2008-09-01

    A fundamental question in biomineralization is the nature of the first-formed mineral phase. In vertebrate bone formation, this issue has been the subject of a long-standing controversy. We address this key issue using the continuously growing fin bony rays of the Tuebingen long-fin zebrafish as a model for bone mineralization. Employing high-resolution scanning and transmission electron microscopy imaging, electron diffraction, and elemental analysis, we demonstrate the presence of an abundant amorphous calcium phosphate phase in the newly formed fin bones. The extracted amorphous mineral particles crystallize with time, and mineral crystallinity increases during bone maturation. Based on these findings, we propose that this amorphous calcium phosphate phase may be a precursor phase that later transforms into the mature crystalline mineral. PMID:18753619

  10. Phase transformations in amorphous fullerite C60 under high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Borisova, P. A.; Blanter, M. S.; Brazhkin, V. V.; Somenkov, V. A.; Filonenko, V. P.

    2015-08-01

    First phase transformations of amorphous fullerite C60 at high temperatures (up to 1800 K) and high pressures (up to 8 GPa) have been investigated and compared with the previous studies on the crystalline fullerite. The study was conducted using neutron diffraction and Raman spectroscopy. The amorphous fullerite was obtained by ball-milling. We have shown that under thermobaric treatment no crystallization of amorphous fullerite into С60 molecular modification is observed, and it transforms into amorphous-like or crystalline graphite. A kinetic diagram of phase transformation of amorphous fullerite in temperature-pressure coordinates was constructed for the first time. Unlike in crystalline fullerite, no crystalline polymerized phases were formed under thermobaric treatment on amorphous fullerite. We found that amorphous fullerite turned out to be less resistant to thermobaric treatment, and amorphous-like or crystalline graphite were formed at lower temperatures than in crystalline fullerite.

  11. Amorphous and microcrystalline silicon technology--1997. Materials Research Society symposium proceedings, Volume 467

    SciTech Connect

    Wagner, S.; Hack, M.; Schiff, E.A.; Schropp, R.; Shimizu, I.

    1997-07-01

    This book was divided into the following parts: Staebler-Wronski and Fundamental Defect Studies in Amorphous Silicon; The Story of Hydrogen in Amorphous Silicon; Photoelectric Properties of Amorphous Silicon; Deposition and Properties of Microcrystalline Silicon; Deposition Studies for Amorphous Silicon and Related Materials; Solar Cells; Thin-Film Transistors; and Sensors and Novel Device Concepts. Separate abstracts were prepared for most of the papers in the volume.

  12. Beating the amorphous limit in thermal conductivity by superlattices design

    PubMed Central

    Mizuno, Hideyuki; Mossa, Stefano; Barrat, Jean-Louis

    2015-01-01

    The value measured in the amorphous structure with the same chemical composition is often considered as a lower bound for the thermal conductivity of any material: the heat carriers are strongly scattered by disorder, and their lifetimes reach the minimum time scale of thermal vibrations. An appropriate design at the nano-scale, however, may allow one to reduce the thermal conductivity even below the amorphous limit. In the present contribution, using molecular-dynamics simulation and the Green-Kubo formulation, we study systematically the thermal conductivity of layered phononic materials (superlattices), by tuning different parameters that can characterize such structures. We have discovered that the key to reach a lower-than-amorphous thermal conductivity is to block almost completely the propagation of the heat carriers, the superlattice phonons. We demonstrate that a large mass difference in the two intercalated layers, or weakened interactions across the interface between layers result in materials with very low thermal conductivity, below the values of the corresponding amorphous counterparts. PMID:26374147

  13. Amorphous metal-organic frameworks for drug delivery.

    PubMed

    Orellana-Tavra, Claudia; Baxter, Emma F; Tian, Tian; Bennett, Thomas D; Slater, Nigel K H; Cheetham, Anthony K; Fairen-Jimenez, David

    2015-09-21

    We report the encapsulation of the hydrophilic model molecule calcein in the Zr-based MOF UiO-66, followed by amorphization of the framework by ball-milling. We show controlled release of calcein over more than 30 days, compared with the 2 day release period from crystalline UiO-66.

  14. Growth induced magnetic anisotropy in crystalline and amorphous thin films

    SciTech Connect

    Hellman, F.

    1998-07-20

    The work in the past 6 months has involved three areas of magnetic thin films: (1) amorphous rare earth-transition metal alloys, (2) epitaxial Co-Pt and Ni-Pt alloy thin films, and (3) collaborative work on heat capacity measurements of magnetic thin films, including nanoparticles and CMR materials. A brief summary of work done in each area is given.

  15. Long-term stability of amorphous-silicon modules

    NASA Astrophysics Data System (ADS)

    Ross, R. G., Jr.

    The Jet Propulsion Laboratory (JPL) program of developing qualification tests necessary for amorphous silicon modules, including appropriate accelerated environmental tests reveal degradation due to illumination. Data were given which showed the results of temperature-controlled field tests and accelerated tests in an environmental chamber.

  16. Thermodynamically controlled crystallization of glucose pentaacetates from amorphous phase

    NASA Astrophysics Data System (ADS)

    Wlodarczyk, P.; Hawelek, L.; Hudecki, A.; Wlodarczyk, A.; Kolano-Burian, A.

    2016-08-01

    The α and β glucose pentaacetates are known sugar derivatives, which can be potentially used as stabilizers of amorphous phase of active ingredients of drugs (API). In the present work, crystallization behavior of equimolar mixture of α and β form in comparison to both pure anomers is revealed. It was shown that despite the same molecular interactions and similar molecular dynamics, crystallization from amorphous phase is significantly suppressed in equimolar mixture. Time dependent X-ray diffraction studies confirmed higher stability of the quenched amorphous equimolar mixture. Its tendency to crystallization is about 10 times lower than for pure anomers. Calorimetric studies revealed that the α and β anomers don't form solid solutions and have eutectic point for xα = 0.625. Suppressed crystallization tendency in the mixture is probably caused by the altered thermodynamics of the system. The factors such as difference of free energy between crystalline and amorphous state or altered configurational entropy are probably responsible for the inhibitory effect.

  17. Impact of surfactants on the crystal growth of amorphous celecoxib.

    PubMed

    Mosquera-Giraldo, Laura I; Trasi, Niraj S; Taylor, Lynne S

    2014-01-30

    The purpose of this study was to investigate the impact of surfactants on the rate of crystal growth of amorphous celecoxib, both in the presence and absence of a polymer. Celecoxib is a poorly water-soluble non-steroidal anti-inflammatory drug. Such compounds may be formulated as amorphous solid dispersions to improve bioavailability, and solid dispersions can contain both a surfactant and a polymer. While the impact of polymers on crystal growth rates has been studied, the effect of surfactants is largely unexplored. Herein, the effect of sodium lauryl sulfate (SLS), sucrose palmitate and d-α tocopherol polyethylenglycol 1000 succinate (TPGS) at a 10% (w/w) concentration on the crystal growth rate of celecoxib was investigated. Linear crystal growth rates as a function of temperature (70-120 °C) were measured using optical microscopy. The mixtures were characterized using differential scanning calorimetry (DSC), infrared spectroscopy, and X-ray diffraction. The results indicate that the surfactants increase the crystal growth rate of amorphous celecoxib. However, addition of polyvinyl pyrrolidone (PVP) helped to mitigate the increase in growth rates, although the ternary systems were highly complex. Thus it is clear that the impact of a surfactant on the physical stability of an amorphous solid dispersion should be considered during formulation.

  18. Nuclear magnetic resonance studies of hydrogen in amorphous silicon

    SciTech Connect

    Norberg, R.E.; Fedders, P.A.; Leopold, D.J.

    1996-12-31

    Proton and deuteron NMR in hydrogenated amorphous silicon yield quantitative measures of species-specific structural configurations and their dynamics. Populations of silicon-bonded and molecular hydrogens correlate with photovoltaic quality, doping, illumination/dark anneal sequences, and with infrared and other characterizations. High quality films contain substantial populations of nanovoid-trapped molecular hydrogen.

  19. 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.

  20. Improved physical stability of amorphous state through acid base interactions.

    PubMed

    Telang, Chitra; Mujumdar, Siddharthya; Mathew, Michael

    2009-06-01

    To investigate role of specific interactions in aiding formation and stabilization of amorphous state in ternary and binary dispersions of a weakly acidic drug. Indomethacin (IMC), meglumine (MU), and polyvinyl pyrollidone (PVP) were the model drug, base, and polymer, respectively. Dispersions were prepared using solvent evaporation. Physical mixtures were cryogenically coground. XRPD, PLM, DSC, TGA, and FTIR were used for characterization. MU has a high crystallization tendency and is characterized by a low T(g) (17 degrees C). IMC crystallization was inhibited in ternary dispersion with MU compared to IMC/PVP alone. An amorphous state formed readily even in coground mixtures. Spectroscopic data are indicative of an IMC-MU amorphous salt and supports solid-state proton transfer. IMC-MU salt displays a low T(g) approximately 50 degrees C, but is more physically stable than IMC, which in molecular mixtures with MU, resisted crystallization even when present in stoichiometric excess of base. This is likely due to a disrupted local structure of amorphous IMC due to specific interactions. IMC showed improved physical stability on incorporating MU in polymer, in spite of low T(g) of the base indicating that chemical interactions play a dominant role in physical stabilization. Salt formation could be induced thermally and mechanically.

  1. 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

  2. Grain boundary resistance to amorphization of nanocrystalline silicon carbide

    NASA Astrophysics Data System (ADS)

    Chen, Dong; Gao, Fei; Liu, Bo

    2015-11-01

    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.

  3. Supercontinuum generation in hydrogenated amorphous silicon waveguides at telecommunication wavelengths.

    PubMed

    Safioui, Jassem; Leo, François; Kuyken, Bart; Gorza, Simon-Pierre; Selvaraja, Shankar Kumar; Baets, Roel; Emplit, Philippe; Roelkens, Gunther; Massar, Serge

    2014-02-10

    We report supercontinuum (SC) generation centered on the telecommunication C-band (1550 nm) in CMOS compatible hydrogenated amorphous silicon waveguides. A broadening of more than 550 nm is obtained in 1cm long waveguides of different widths using as pump picosecond pulses with on chip peak power as low as 4 W.

  4. Modeling of amorphous carbon structures with arbitrary structural constraints.

    PubMed

    Jornada, F H; Gava, V; Martinotto, A L; Cassol, L A; Perottoni, C A

    2010-10-01

    In this paper we describe a method to generate amorphous structures with arbitrary structural constraints. This method employs the simulated annealing algorithm to minimize a simple yet carefully tailored cost function (CF). The cost function is composed of two parts: a simple harmonic approximation for the energy-related terms and a cost that penalizes configurations that do not have atoms in the desired coordinations. Using this approach, we generated a set of amorphous carbon structures spawning nearly all the possible combinations of sp, sp(2) and sp(3) hybridizations. The bulk moduli of this set of amorphous carbons structures was calculated using Brenner's potential. The bulk modulus strongly depends on the mean coordination, following a power-law behavior with an exponent ν = 1.51 ± 0.17. A modified cost function that segregates carbon with different hybridizations is also presented, and another set of structures was generated. With this new set of amorphous materials, the correlation between the bulk modulus and the mean coordination weakens. The method proposed can be easily modified to explore the effects on the physical properties of the presence of hydrogen, dangling bonds, and structural features such as carbon rings.

  5. Structural origin of resistance drift in amorphous GeTe

    NASA Astrophysics Data System (ADS)

    Zipoli, Federico; Krebs, Daniel; Curioni, Alessandro

    2016-03-01

    We used atomistic simulations to study the origin of the change of resistance over time in the amorphous phase of GeTe, a prototypical phase-change material (PCM). Understanding the cause of resistance drift is one of the biggest challenges to improve multilevel storage technology. For this purpose, we generated amorphous structures via classical molecular-dynamics simulations under conditions as close as possible to the experimental operating ones of such memory devices. Moreover, we used the replica-exchange technique to generate structures comparable with those obtained in the experiment after long annealing that show an increase of resistance. This framework allowed us to overcome the main limitation of previous simulations, based on density-functional theory, that suffered from being computationally too expensive therefore limited to the nanosecond time scale. We found that resistance drift is caused by consumption of Ge atom clusters in which the coordination of at least one Ge atom differs from that of the crystalline phase and by removal of stretched bonds in the amorphous network, leading to a shift of the Fermi level towards the middle of the band gap. These results show that one route to design better memory devices based on current chalcogenide alloys is to reduce the resistance drift by increasing the rigidity of the amorphous network.

  6. Amorphous Silk Fibroin Membranes for Separation of CO2

    NASA Technical Reports Server (NTRS)

    Aberg, Christopher M.; Patel, Anand K.; Gil, Eun Seok; Spontak, Richard J.; Hagg, May-Britt

    2009-01-01

    Amorphous silk fibroin has shown promise as a polymeric material derivable from natural sources for making membranes for use in removing CO2 from mixed-gas streams. For most applications of silk fibroin, for purposes other than gas separation, this material is used in its highly crystalline, nearly natural form because this form has uncommonly high tensile strength. However, the crystalline phase of silk fibroin is impermeable, making it necessary to convert the material to amorphous form to obtain the high permeability needed for gas separation. Accordingly, one aspect of the present development is a process for generating amorphous silk fibroin by treating native silk fibroin in an aqueous methanol/salt solution. The resulting material remains self-standing and can be prepared as thin film suitable for permeation testing. The permeability of this material by pure CO2 has been found to be highly improved, and its mixed-gas permeability has been found to exceed the mixed-gas permeabilities of several ultrahigh-CO2-permeable synthetic polymers. Only one of the synthetic polymers poly(trimethylsilylpropyne) [PTMSP] may be more highly permeable by CO2. PTMSP becomes unstable with time, whereas amorphous silk should not, although at the time of this reporting this has not been conclusively proven.

  7. Grain boundary resistance to amorphization of nanocrystalline silicon carbide.

    PubMed

    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

  8. Density driven structural transformations in amorphous semiconductor clathrates

    DOE PAGES

    Tulk, Christopher A.; dos Santos, Antonio M.; Neuefeind, Joerg C.; Molaison, Jamie J.; Sales, Brian C.; Honkimaeki, Veijo

    2015-01-16

    The pressure induced crystalline collapse at 14.7 GPa and polyamorphic structures of the semiconductor clathrate Sr8Ga16Ge30 are reported up to 35 GPa. In-situ total scattering measurements under pressure allow the direct microscopic inspection of the mechanisms associated with pressure induced amorphization in these systems, as well as the structure of the recovered phase. It is observed that, between 14.7 and 35 GPa the second peak in the structure factor function gradually disappears. Analysis of the radial distribution function extracted from those data indicate that this feature is associated with gradual cage collapse and breakdown of the tetrahedral structure with themore » consequent systematic lengthening of the nearest-neighbor framework bonds. This suggests an overall local coordination change to an even higher density amorphous form. Upon recovery from high pressure, the sample remains amorphous, and while there is some indication of the guest-host cage reforming, it doesn't seem that the tetrahedral coordination is recovered. As such, the compresion-decompression process in this systems gives rise to three distict amorphous forms.« less

  9. Density driven structural transformations in amorphous semiconductor clathrates

    SciTech Connect

    Tulk, Christopher A.; dos Santos, Antonio M.; Neuefeind, Joerg C.; Molaison, Jamie J.; Sales, Brian C.; Honkimaeki, Veijo

    2015-01-16

    The pressure induced crystalline collapse at 14.7 GPa and polyamorphic structures of the semiconductor clathrate Sr8Ga16Ge30 are reported up to 35 GPa. In-situ total scattering measurements under pressure allow the direct microscopic inspection of the mechanisms associated with pressure induced amorphization in these systems, as well as the structure of the recovered phase. It is observed that, between 14.7 and 35 GPa the second peak in the structure factor function gradually disappears. Analysis of the radial distribution function extracted from those data indicate that this feature is associated with gradual cage collapse and breakdown of the tetrahedral structure with the consequent systematic lengthening of the nearest-neighbor framework bonds. This suggests an overall local coordination change to an even higher density amorphous form. Upon recovery from high pressure, the sample remains amorphous, and while there is some indication of the guest-host cage reforming, it doesn't seem that the tetrahedral coordination is recovered. As such, the compresion-decompression process in this systems gives rise to three distict amorphous forms.

  10. Beating the amorphous limit in thermal conductivity by superlattices design.

    PubMed

    Mizuno, Hideyuki; Mossa, Stefano; Barrat, Jean-Louis

    2015-09-16

    The value measured in the amorphous structure with the same chemical composition is often considered as a lower bound for the thermal conductivity of any material: the heat carriers are strongly scattered by disorder, and their lifetimes reach the minimum time scale of thermal vibrations. An appropriate design at the nano-scale, however, may allow one to reduce the thermal conductivity even below the amorphous limit. In the present contribution, using molecular-dynamics simulation and the Green-Kubo formulation, we study systematically the thermal conductivity of layered phononic materials (superlattices), by tuning different parameters that can characterize such structures. We have discovered that the key to reach a lower-than-amorphous thermal conductivity is to block almost completely the propagation of the heat carriers, the superlattice phonons. We demonstrate that a large mass difference in the two intercalated layers, or weakened interactions across the interface between layers result in materials with very low thermal conductivity, below the values of the corresponding amorphous counterparts.

  11. Amorphous-silicon solar cells with screen-printed metallization

    NASA Astrophysics Data System (ADS)

    Baert, Kris A.; Roggen, J.; Nijs, Johan F.; Mertens, Robert P.

    1990-03-01

    The use of screen printing for the back-side metallization of amorphous-silicon solar cells on glass is proposed. Compared with the conventional aluminum evaporation process, screen printing is attractive because it offers high throughput and because direct patterning is performed during the printing process. The critical point in realizing a thick-film screen-printed contact on amorphous-silicon solar cells is found to be the contact resistivity between the contact and the n-layer. Contact resistivities below 1 ohm-sq cm have been obtained using a microcrystalline instead of an amorphous n+ layer and a screen-printed contact based on Mo, Ti, or Ni. Amorphous-silicon solar cells with a screen-printed back contact had a performance comparable with that of cells with an evaporated Al contact, resulting in a efficiency of 9.7 percent. Spectral response measurements demonstrated that the screen-printed contact is an efficient reflector of long-wavelength photons, resulting in a high red response due to internal light trapping.

  12. Photostability of crystalline versus amorphous nifedipine and nimodipine.

    PubMed

    Grooff, Driekus; Francis, Farzaana; De Villiers, Melgardt M; Ferg, Ernst

    2013-06-01

    True solid-state photostability of the drugs nifedipine and nimodipine was investigated during exposure to UV-visible radiation. Photostability was studied on a small scale as thin films of approximately 1 mg drug, which contained either amorphous or re-crystallised stable phases. High-performance liquid chromatography analysis revealed a greater rate and extent of decomposition for the amorphous phases. Photoexposed amorphous nifedipine exhibited approximately 1.8-fold larger first-order decomposition rate constant (k) relative to its crystalline phase. The increase in k was more significant for photoexposed amorphous nimodipine at approximately sixfold relative to its crystalline phase. Photodecomposition in scaled-up samples of the stable crystalline phases for both drugs was monitored with X-ray diffraction in Bragg-Brentano geometry. The similarities in the calculated photodecomposition extents to results from small scale validated the specificity of the X-ray analysis technique to the photodecomposition region. The considerably faster decomposition rates in small-scale studies were attributed to a maximised surface area (A) for quantity (m0 ) of exposed drug. Kinetic interpretations of true solid-state stability should consider the sample solid dimensions in terms of the direct exposed A and m0 in the photodecomposition region, that is, outer layers in solid.

  13. Radiation-induced amorphization of rare-earth titanate pyrochlores

    NASA Astrophysics Data System (ADS)

    Lian, Jie; Chen, Jian; Wang, L. M.; Ewing, Rodney C.; Farmer, J. Matt; Boatner, Lynn A.; Helean, K. B.

    2003-10-01

    Single crystals of the entire series of A2Ti2O7 (A=Sm to Lu, and Y) pyrochlore compounds were irradiated by 1-MeV Kr+ ions at temperatures from 293 to 1073 K, and the microstructure evolution, as a function of increasing radiation fluence, was characterized using in situ transmission electron microscopy (TEM). The critical amorphization temperature, Tc, generally increases from ˜480 to ˜1120 K with increasing A-site cation size (e.g., 0.977 Å for Lu3+ to 1.079 Å for Sm3+). An abnormally high susceptibility to ion beam damage was found for Gd2Ti2O7 (with the highest Tc of ˜1120 K). Factors influencing the response of titanate pyrochlores to ion irradiation-induced amorphization are discussed in terms of cation radius ratio, defect formation, and the tendency to undergo an order-disorder transition to the defect-fluorite structure. The resistance of the pyrochlore structure to ion beam-induced amorphization is not only affected by the relative sizes of the A- and B-site cations, but also the cation electronic configuration and the structural disorder. Pyrochlore compositions that have larger structural deviations from the ideal fluorite structure, as evidenced by the smaller 48f oxygen positional parameter, x, are more sensitive to ion beam-induced amorphization.

  14. Photocurrent images of amorphous-silicon solar-cell modules

    NASA Technical Reports Server (NTRS)

    Kim, Q.; Shumka, A.; Trask, J.

    1985-01-01

    Results obtained in applying the unique characteristics of the solar cell laser scanner to investigate the defects and quality of amorphous silicon cells are presented. It is concluded that solar cell laser scanners can be effectively used to nondestructively test not only active defects but also the cell quality and integrity of electrical contacts.

  15. Method of depositing wide bandgap amorphous semiconductor materials

    DOEpatents

    Ellis, Jr., Frank B.; Delahoy, Alan E.

    1987-09-29

    A method of depositing wide bandgap p type amorphous semiconductor materials on a substrate without photosensitization by the decomposition of one or more higher order gaseous silanes in the presence of a p-type catalytic dopant at a temperature of about 200.degree. C. and a pressure in the range from about 1-50 Torr.

  16. Earthquake lubrication and healing explained by amorphous nanosilica

    NASA Astrophysics Data System (ADS)

    Rowe, C. D.; Lamothe, K. G.; Rempe, M.; Andrews, M.; Mitchell, T. M.; Di Toro, G.; White, J. C.

    2015-12-01

    Earthquake slip and rupture propagation require fault strength to decrease during slip. Extreme shear weakening observed in laboratory friction experiments on silica-rich rocks has been explained by the formation of a hydrated amorphous 'silica gel' on the slip surface, but the mode of formation and deformation behavior of this material are not known. In addition, the wear material displays time-dependent strengthening on timescales of hours to days. We performed shearing experiments on chert rocks and analyzed the wear material formed at a range of slip rates from 10-4 - 10-1 m/s. We show by transmission electron microscopy (TEM) and X-ray diffraction that silica lubrication is the result of the formation of amorphous nanopowder rather than a gel. The nanopowder has distinct structure and properties when compared to commercially available amorphous silica nanoparticles, which result from the degree and distribution of hydration and the style of bond strain within particles (observed by Raman spectroscopy and FTIR). The lubrication effect is due to intra-particle plasticity, even at low temperature and interparticle lubrication caused by trapping of water layers between hydrated surfaces. The hours to days timescale of healing may be explained by the natural time-dependent sintering between the hydrated surfaces of the nanopowder. Formation of amorphous silica nanopowders during slip can explain the general characteristics of earthquake ruptures, including the timescales of coseismic weakening and post-seismic healing.

  17. Universal amorphous-amorphous transition in GexSe100‑x glasses under pressure

    NASA Astrophysics Data System (ADS)

    Yildirim, Can; Micoulaut, Matthieu; Boolchand, Punit; Kantor, Innokenty; Mathon, Olivier; Gaspard, Jean-Pierre; Irifune, Tetsuo; Raty, Jean-Yves

    2016-06-01

    Pressure induced structural modifications in vitreous GexSe100‑x (where 10 ≤ x ≤ 25) are investigated using X-ray absorption spectroscopy (XAS) along with supplementary X-ray diffraction (XRD) experiments and ab initio molecular dynamics (AIMD) simulations. Universal changes in distances and angle distributions are observed when scaled to reduced densities. All compositions are observed to remain amorphous under pressure values up to 42 GPa. The Ge-Se interatomic distances extracted from XAS data show a two-step response to the applied pressure; a gradual decrease followed by an increase at around 15–20 GPa, depending on the composition. This increase is attributed to the metallization event that can be traced with the red shift in Ge K edge energy which is also identified by the principal peak position of the structure factor. The densification mechanisms are studied in details by means of AIMD simulations and compared to the experimental results. The evolution of bond angle distributions, interatomic distances and coordination numbers are examined and lead to similar pressure-induced structural changes for any composition.

  18. Universal amorphous-amorphous transition in GexSe100−x glasses under pressure

    PubMed Central

    Yildirim, Can; Micoulaut, Matthieu; Boolchand, Punit; Kantor, Innokenty; Mathon, Olivier; Gaspard, Jean-Pierre; Irifune, Tetsuo; Raty, Jean-Yves

    2016-01-01

    Pressure induced structural modifications in vitreous GexSe100−x (where 10 ≤ x ≤ 25) are investigated using X-ray absorption spectroscopy (XAS) along with supplementary X-ray diffraction (XRD) experiments and ab initio molecular dynamics (AIMD) simulations. Universal changes in distances and angle distributions are observed when scaled to reduced densities. All compositions are observed to remain amorphous under pressure values up to 42 GPa. The Ge-Se interatomic distances extracted from XAS data show a two-step response to the applied pressure; a gradual decrease followed by an increase at around 15–20 GPa, depending on the composition. This increase is attributed to the metallization event that can be traced with the red shift in Ge K edge energy which is also identified by the principal peak position of the structure factor. The densification mechanisms are studied in details by means of AIMD simulations and compared to the experimental results. The evolution of bond angle distributions, interatomic distances and coordination numbers are examined and lead to similar pressure-induced structural changes for any composition. PMID:27273197

  19. Bivalves build their shells from amorphous calcium carbonate

    NASA Astrophysics Data System (ADS)

    Jacob, D. E.; Wirth, R.; Soldati, A. L.; Wehrmeister, U.

    2012-04-01

    One of the most common shell structures in the bivalve class is the prism and nacre structure. It is widely distributed amongst both freshwater and marine species and gives cultured pearls their sought-after lustre. In freshwater bivalves, both shell structures (prism and nacre) consist of aragonite. Formation of the shell form an amorphous precursor phase is a wide-spread strategy in biomineralization and presents a number of advantages for the organisms in the handling of the CaCO3 material. While there is already evidence that larval shells of some mollusk species use amorphous calcium carbonate (ACC) as a transient precursor phase for aragonite, the use of this strategy by adult animals was only speculated upon. We present results from in-situ geochemistry, Raman spectroscopy and focused-ion beam assisted TEM on three species from two different bivalve families that show that remnants of ACC can be found in shells from adult species. We show that the amorphous phase is not randomly distributed, but is systematically found in a narrow zone at the interface between periostracum and prism layer. This zone is the area where spherulitic CaCO3- structures protrude from the inner periostracum to form the initial prisms. These observations are in accordance with our earlier results on equivalent structures in freshwater cultured pearls (Jacob et al., 2008) and show that the original building material for the prisms is amorphous calcium carbonate, secreted in vesicles at the inner periostracum layer. Quantitative temperature calibrations for paleoclimate applications using bivalve shells are based on the Mg-Ca exchange between inorganic aragonite (or calcite) and water. These calibrations, thus, do not take into account the biomineral crystallization path via an amorphous calcium carbonate precursor and are therefore likely to introduce a bias (a so-called vital effect) which currently is not accounted for. Jacob et al. (2008) Geochim. Cosmochim. Acta 72, 5401-5415

  20. Amorphous-silicon thin-film heterojunction solar cells

    SciTech Connect

    Cretella, M. C.; Gregory, J. A.; Sandstrom, D. B.; Paul, W.

    1981-01-01

    The investigation of amorphous silicon materials at MTSEC has had two major thrusts: (1) to improve the amorphous material, i.e., obtain a low state density in the gap, improve the carrier collection depth and diminish non-radiative recombinations; and (2) to attempt to understand and improve on the limitations of the junction devices while evaluating the amorphous silicon materials. In the first of these efforts, the investigation has continued to examine the modifications to the a-Si(H) network by alloying silicon with other group IVA elements, either in binary or ternary compositions, and/or by replacing the hydrogenation for defect compensation with a combination of hydrogenation and alkylation or hydrogenation and halogenation. The doped junction layers are being examined in an attempt to determine the limiting characteristics of the junctions in solar cell devices of these amorphous materials. Amorphous alloys of Si-Ge, Si-C, Si-Sn were prepared as well as ternary compositions of Si-Ge-C and Si-Sn-C. In addition, Na vapor was added to the gas feed to deposit a-Si(Na, H) films, and to prepare Si-Sn, fluoride was added along with the tin by vapor additions of SnF/sub 4/ to the gas feed. The optical properties of these materials were measured, and structural and compositional information was obtained from the IR vibrational spectra using the scanning electron microscope and from analyses using scanning Auger microscopy. Electrical measurements have included the dark conductivity and the photo conductivity under room fluorescent light and at AM1 conditions. With alloys that displayed promising photoconductive properties n-i-p devices were prepared to assess the solar cell properties. Details are presented. (WHK)

  1. Fluctuation Electron Microscopy of Amorphous and Polycrystalline Materials

    NASA Astrophysics Data System (ADS)

    Rezikyan, Aram

    Fluctuation Electron Microscopy (FEM) has become an effective materials' structure characterization technique, capable of probing medium-range order (MRO) that may be present in amorphous materials. Although its sensitivity to MRO has been exercised in numerous studies, FEM is not yet a quantitative technique. The holdup has been the discrepancy between the computed kinematical variance and the experimental variance, which previously was attributed to source incoherence. Although high-brightness, high coherence, electron guns are now routinely available in modern electron microscopes, they have not eliminated this discrepancy between theory and experiment. The main objective of this thesis was to explore, and to reveal, the reasons behind this conundrum. The study was started with an analysis of the speckle statistics of tilted dark-field TEM images obtained from an amorphous carbon sample, which confirmed that the structural ordering is sensitively detected by FEM. This analysis also revealed the inconsistency between predictions of the source incoherence model and the experimentally observed variance. FEM of amorphous carbon, amorphous silicon and ultra nanocrystalline diamond samples was carried out in an attempt to explore the conundrum. Electron probe and sample parameters were varied to observe the scattering intensity variance behavior. Results were compared to models of probe incoherence, diffuse scattering, atom displacement damage, energy loss events and multiple scattering. Models of displacement decoherence matched the experimental results best. Decoherence was also explored by an interferometric diffraction method using bilayer amorphous samples, and results are consistent with strong displacement decoherence in addition to temporal decoherence arising from the electron source energy spread and energy loss events in thick samples. It is clear that decoherence plays an important role in the long-standing discrepancy between experimental FEM and its

  2. Effect of amorphous lamella on the crack propagation behavior of crystalline Mg/amorphous Mg-Al nanocomposites

    NASA Astrophysics Data System (ADS)

    Hai-Yang, Song; Yu-Long, Li

    2016-02-01

    The effects of amorphous lamella on the crack propagation behavior in crystalline/amorphous (C/A) Mg/Mg-Al nanocomposites under tensile loading are investigated using the molecular dynamics simulation method. The sample with an initial crack of orientation [0001] is considered here. For the nano-monocrystal Mg, the crack growth exhibits brittle cleavage. However, for the C/A Mg/Mg-Al nanocomposites, the ‘double hump’ behavior can be observed in all the stress-strain curves regardless of the amorphous lamella thickness. The results indicate that the amorphous lamella plays a critical role in the crack deformation, and it can effectively resist the crack propagation. The above mentioned crack deformation behaviors are also disclosed and analyzed in the present work. The results here provide a strategy for designing the high-performance hexagonal-close-packed metal and alloy materials. Project supported by the National Natural Science Foundation of China (Grant Nos. 11372256 and 11572259), the 111 Project (Grant No. B07050), the Program for New Century Excellent Talents in University of Ministry of Education of China (Grant No. NCET-12-1046), and the Program for New Scientific and Technological Star of Shaanxi Province, China (Grant No. 2012KJXX-39).

  3. Phase diagram of amorphous solid water: low-density, high-density, and very-high-density amorphous ices.

    PubMed

    Giovambattista, Nicolas; Stanley, H Eugene; Sciortino, Francesco

    2005-09-01

    We calculate the phase diagram of amorphous solid water by performing molecular dynamics simulations using the extended simple point charge (SPC/E) model. Our simulations follow different paths in the phase diagram: isothermal compression/decompression, isochoric cooling/heating, and isobaric cooling/heating. We are able to identify low-density amorphous (LDA), high-density amorphous (HDA), and very-high density amorphous (VHDA) ices. The density rho of these glasses at different pressure P and temperature T agree well with experimental values. We also study the radial distribution functions of glassy water. In agreement with experiments, we find that LDA, HDA, and VHDA are characterized by a tetrahedral hydrogen-bonded network and that, as compared to LDA, HDA has an extra interstitial molecule between the first and second shell. VHDA appears to have two such extra molecules. We obtain VHDA, as in experiment, by isobaric heating of HDA. We also find that "other forms" of glassy water can be obtained upon isobaric heating of LDA, as well as amorphous ices formed during the transformation of LDA to HDA. We argue that these other forms of amorphous ices, as well as VHDA, are not altogether new glasses but rather are the result of aging induced by heating. Samples of HDA and VHDA with different densities are recovered at normal P, showing that there is a continuum of glasses. Furthermore, the two ranges of densities of recovered HDA and recovered VHDA overlap at ambient P. Our simulations reproduce the experimental findings of HDA --> LDA and VHDA --> LDA transformations. We do not observe a VHDA --> HDA transformation, and our final phase diagram of glassy water together with equilibrium liquid data suggests that for the SPC/E model the VHDA --> HDA transformation cannot be observed with the present heating rates accessible in simulations. Finally, we discuss the consequences of our findings for the understanding of the transformation between the different amorphous

  4. Amorphous metal formulations and structured coatings for corrosion and wear resistance

    DOEpatents

    Farmer, Joseph C.

    2011-12-13

    A system for coating a surface comprising providing a source of amorphous metal that contains more than 11 elements and applying the amorphous metal that contains more than 11 elements to the surface by a spray. Also a coating comprising a composite material made of amorphous metal that contains more than 11 elements. An apparatus for producing a corrosion-resistant amorphous-metal coating on a structure comprises a deposition chamber, a deposition source in the deposition chamber that produces a deposition spray, the deposition source containing a composite material made of amorphous metal that contains more than 11 elements, and a system that directs the deposition spray onto the structure.

  5. Amorphous metal formulations and structured coatings for corrosion and wear resistance

    DOEpatents

    Farmer, Joseph C.

    2014-07-15

    A system for coating a surface comprising providing a source of amorphous metal that contains more than 11 elements and applying the amorphous metal that contains more than 11 elements to the surface by a spray. Also a coating comprising a composite material made of amorphous metal that contains more than 11 elements. An apparatus for producing a corrosion-resistant amorphous-metal coating on a structure comprises a deposition chamber, a deposition source in the deposition chamber that produces a deposition spray, the deposition source containing a composite material made of amorphous metal that contains more than 11 elements, and a system that directs the deposition spray onto the structure.

  6. Experimental Evidence for a Crossover between Two Distinct Mechanisms of Amorphization in Ice Ih under Pressure

    SciTech Connect

    Straessle, Thierry; Klotz, Stefan; Hamel, Gerard; Koza, Michael M.; Schober, Helmut

    2007-10-26

    We report neutron scattering data which reveal the central role of phonon softening leading to a negative melting line, solid-state amorphization, and negative thermal expansion of ice. We find that pressure-induced amorphization is due to mechanical melting at low temperatures, while at higher temperatures amorphization is governed by thermal melting (violations of Born's and Lindemann's criteria, respectively). This confirms earlier conjectures of a crossover between two distinct amorphization mechanisms and provides a natural explanation for the strong annealing observed in high-density amorphous ice.

  7. Adsorption of selenium by amorphous iron oxyhydroxide and manganese dioxide

    USGS Publications Warehouse

    Balistrieri, L.S.; Chao, T.T.

    1990-01-01

    This work compares and models the adsorption of selenium and other anions on a neutral to alkaline surface (amorphous iron oxyhydroxide) and an acidic surface (manganese dioxide). Selenium adsorption on these oxides is examined as a function of pH, particle concentration, oxidation state, and competing anion concentration in order to assess how these factors might influence the mobility of selenium in the environment. The data indicate that 1. 1) amorphous iron oxyhydroxide has a greater affinity for selenium than manganese dioxide, 2. 2) selenite [Se(IV)] adsorption increases with decreasing pH and increasing particle concentration and is stronger than selenate [Se(VI)] adsorption on both oxides, and 3. 3) selenate does not adsorb on manganese dioxide. The relative affinity of selenate and selenite for the oxides and the lack of adsorption of selenate on a strongly acidic surface suggests that selenate forms outer-sphere complexes while selenite forms inner-sphere complexes with the surfaces. The data also indicate that the competition sequence of other anions with respect to selenite adsorption at pH 7.0 is phosphate > silicate > molybdate > fluoride > sulfate on amorphous iron oxyhydroxide and molybdate ??? phosphate > silicate > fluoride > sulfate on manganese dioxide. The adsorption of phosphate, molybdate, and silicate on these oxides as a function of pH indicates that the competition sequences reflect the relative affinities of these anions for the surfaces. The Triple Layer surface complexation model is used to provide a quantitative description of these observations and to assess the importance of surface site heterogeneity on anion adsorption. The modeling results suggest that selenite forms binuclear, innersphere complexes with amorphous iron oxyhydroxide and monodentate, inner-sphere complexes with manganese dioxide and that selenate forms outer-sphere, monodentate complexes with amorphous iron oxyhydroxide. The heterogeneity of the oxide surface sites

  8. Diffusion and the Thermal Stability of Amorphous Copper-Zirconium

    NASA Astrophysics Data System (ADS)

    Stelter, Eric Carl

    Measurements have been made of diffusion and thermal relaxation in amorphous Cu(,50)Zr(,50). Samples were prepared by melt-spinning under vacuum. Diffusion measurements were made over the temperature range from 317 to 385 C, using Ag and Au as substitutional impurities, by means of Auger electron spectrometry (AES) and Rutherford backscattering spectrometry (RBS). Thermal measurements were made by differential scanning calorimetry (DSC) up to 550 C. The diffusion coefficients of Ag and Au in amorphous Cu(,50)Zr(,50) are found to be somewhat higher than, but very close in magnitude to the coefficient of self-diffusion in crystalline Cu at the same temperatures. The activation energies for diffusion in the amorphous alloy are 0.72 to 1.55 eV/atom, much closer to the activation energy for self-diffusion in liquid Cu, 0.42 eV/atom, than that for the crystalline solid, 2.19 eV/atom. The mechanism for diffusion in the amorphous metal is presumably quite different from the monovacancy mechanism dominant in the crystalline solid. The pre-exponential terms are found to be extremely small, on the order of 10('-10) to 10('-11) cm('2)/sec for Ag diffusion. This indicates that diffusion in amorphous Cu(,50)Zr(,50) may involve an extended defect of 10 or more atoms. Analysis of the data in terms of the free -volume model also lends strength to this conclusion and indicates that the glass is composed of liquid-like clusters of 15 to 20 atoms. The initial stage of relaxation in amorphous CuZr occurs with a spectrum of activation energies. The lowest activation energy involved, 0.78 eV/atom, is almost identical to the average activation energy of Ag diffusion in the glass, 0.77 eV/atom, indicating that relaxation occurs primarily through diffusion. The activation energy of crystallization, determined by Kissinger's method, is 3.10 eV/atom. The large difference, on the order of 2.3 eV/atom, between the activation energies of crystallization and diffusion is attributed to the energy

  9. Correlation of atomic packing with the boson peak in amorphous alloys

    SciTech Connect

    Yang, W. M.; Liu, H. S. E-mail: blshen@seu.edu.cn E-mail: jiangjz@zju.edu.cn; Zhao, Y. C.; Liu, X. J.; Chen, G. X.; Man, Q. K.; Chang, C. T.; Li, R. W. E-mail: blshen@seu.edu.cn E-mail: jiangjz@zju.edu.cn; Dun, C. C.; Shen, B. L. E-mail: blshen@seu.edu.cn E-mail: jiangjz@zju.edu.cn; Inoue, A.; and others

    2014-09-28

    Boson peaks (BP) have been observed from phonon specific heats in 10 studied amorphous alloys. Two Einstein-type vibration modes were proposed in this work and all data can be fitted well. By measuring and analyzing local atomic structures of studied amorphous alloys and 56 reported amorphous alloys, it is found that (a) the BP originates from local harmonic vibration modes associated with the lengths of short-range order (SRO) and medium-range order (MRO) in amorphous alloys, and (b) the atomic packing in amorphous alloys follows a universal scaling law, i.e., the ratios of SRO and MRO lengths to solvent atomic diameter are 3 and 7, respectively, which exact match with length ratios of BP vibration frequencies to Debye frequency for the studied amorphous alloys. This finding provides a new perspective for atomic packing in amorphous materials, and has significant implications for quantitative description of the local atomic orders and understanding the structure-property relationship.

  10. Characterization of melt-quenched and milled amorphous solids of gatifloxacin.

    PubMed

    Hattori, Yusuke; Suzuki, Ayumi; Otsuka, Makoto

    2016-11-01

    The objectives of this study were to characterize and investigate the differences in amorphous states of gatifloxacin. We prepared two types of gatifloxacin amorphous solids coded as M and MQ using milling and melt-quenching methods, respectively. The amorphous solids were characterized via X-ray diffraction (XRD), nonisothermal differential scanning calorimetry (DSC) and time-resolved near-infrared (NIR) spectroscopy. Both the solids displayed halo XRD patterns, the characteristic of amorphous solids; however, in the non-isothermal DSC profiles, these amorphous solids were distinguished by their crystallization and melting temperatures. The Kissinger-Akahira-Sunose plots of non-isothermal crystallization temperatures at various heating rates indicated a lower activation energy of crystallization for the amorphous solid M than that of MQ. These results support the differentiation between two amorphous states with different physical and chemical properties.

  11. Coaxial carbon plasma gun deposition of amorphous carbon films

    NASA Technical Reports Server (NTRS)

    Sater, D. M.; Gulino, D. A.; Rutledge, S. K.

    1984-01-01

    A unique plasma gun employing coaxial carbon electrodes was used in an attempt to deposit thin films of amorphous diamond-like carbon. A number of different structural, compositional, and electrical characterization techniques were used to characterize these films. These included scanning electron microscopy, scanning transmission electron microscopy, X ray diffraction and absorption, spectrographic analysis, energy dispersive spectroscopy, and selected area electron diffraction. Optical absorption and electrical resistivity measurements were also performed. The films were determined to be primarily amorphous, with poor adhesion to fused silica substrates. Many inclusions of particulates were found to be present as well. Analysis of these particulates revealed the presence of trace impurities, such as Fe and Cu, which were also found in the graphite electrode material. The electrodes were the source of these impurities. No evidence of diamond-like crystallite structure was found in any of the film samples. Details of the apparatus, experimental procedure, and film characteristics are presented.

  12. Force-field parameters for beryllium complexes in amorphous layers.

    PubMed

    Emelyanova, Svetlana; Chashchikhin, Vladimir; Bagaturyants, Alexander

    2016-09-01

    Unknown force-field parameters for metal organic beryllium complexes used in emitting and electron transporting layers of OLED structures are determined. These parameters can be used for the predictive atomistic simulations of the structure and properties of amorphous organic layers containing beryllium complexes. The parameters are found for the AMBER force field using a relaxed scan procedure and quantum-mechanical DFT calculations of potential energy curves for specific internal (angular) coordinates in a series of three Be complexes (Bebq2; Be(4-mpp)2; Bepp2). The obtained parameters are verified in calculations of some molecular and crystal structures available from either quantum-mechanical DFT calculations or experimental data. Graphical Abstract Beryllium complexes in amorphous layersᅟ. PMID:27550375

  13. Solution-processed amorphous silicon surface passivation layers

    SciTech Connect

    Mews, Mathias Sontheimer, Tobias; Korte, Lars; Rech, Bernd; Mader, Christoph; Traut, Stephan; Wunnicke, Odo

    2014-09-22

    Amorphous silicon thin films, fabricated by thermal conversion of neopentasilane, were used to passivate crystalline silicon surfaces. The conversion is investigated using X-ray and constant-final-state-yield photoelectron spectroscopy, and minority charge carrier lifetime spectroscopy. Liquid processed amorphous silicon exhibits high Urbach energies from 90 to 120 meV and 200 meV lower optical band gaps than material prepared by plasma enhanced chemical vapor deposition. Applying a hydrogen plasma treatment, a minority charge carrier lifetime of 1.37 ms at an injection level of 10{sup 15}/cm{sup 3} enabling an implied open circuit voltage of 724 mV was achieved, demonstrating excellent silicon surface passivation.

  14. Plastic response and correlations in athermally sheared amorphous solids

    NASA Astrophysics Data System (ADS)

    Puosi, F.; Rottler, J.; Barrat, J.-L.

    2016-09-01

    The onset of irreversible deformation in low-temperature amorphous solids is due to the accumulation of elementary events, consisting of spatially and temporally localized atomic rearrangements involving only a few tens of atoms. Recently, numerical and experimental work addressed the issue of spatiotemporal correlations between these plastic events. Here, we provide further insight into these correlations by investigating, via molecular dynamics (MD) simulations, the plastic response of a two-dimensional amorphous solid to artificially triggered local shear transformations. We show that while the plastic response is virtually absent in as-quenched configurations, it becomes apparent if a shear strain was previously imposed on the system. Plastic response has a fourfold symmetry, which is characteristic of the shear stress redistribution following the local transformation. At high shear rate we report evidence for a fluctuation-dissipation relation, connecting plastic response and correlation, which seems to break down if lower shear rates are considered.

  15. Amorphous tin-cadmium oxide films and the production thereof

    SciTech Connect

    Li, Xiaonan; Gessert, Timothy A

    2013-10-29

    A tin-cadmium oxide film having an amorphous structure and a ratio of tin atoms to cadmium atoms of between 1:1 and 3:1. The tin-cadmium oxide film may have an optical band gap of between 2.7 eV and 3.35 eV. The film may also have a charge carrier concentration of between 1.times.10.sup.20 cm.sup.-3 and 2.times.10.sup.20 cm.sup.-3. The tin cadmium oxide film may also exhibit a Hall mobility of between 40 cm.sup.2V.sup.-1 s.sup.-1 and 60 cm.sup.2V.sup.-1 s.sup.-1. Also disclosed is a method of producing an amorphous tin-cadmium oxide film as described and devices using same.

  16. Self-assembly of amorphous calcium carbonate microlens arrays

    PubMed Central

    Lee, Kyubock; Wagermaier, Wolfgang; Masic, Admir; Kommareddy, Krishna P.; Bennet, Mathieu; Manjubala, Inderchand; Lee, Seung-Woo; Park, Seung B.; Cölfen, Helmut; Fratzl, Peter

    2012-01-01

    Biological materials are often based on simple constituents and grown by the principle of self-assembly under ambient conditions. In particular, biomineralization approaches exploit efficient pathways of inorganic material synthesis. There is still a large gap between the complexity of natural systems and the practical utilization of bioinspired formation mechanisms. Here we describe a simple self-assembly route leading to a CaCO3 microlens array, somewhat reminiscent of the brittlestars' microlenses, with uniform size and focal length, by using a minimum number of components and equipment at ambient conditions. The formation mechanism of the amorphous CaCO3 microlens arrays was elucidated by confocal Raman spectroscopic imaging to be a two-step growth process mediated by the organic surfactant. CaCO3 microlens arrays are easy to fabricate, biocompatible and functional in amorphous or more stable crystalline forms. This shows that advanced optical materials can be generated by a simple mineral precipitation. PMID:22395616

  17. Coexistence of amorphous and crystalline calcium carbonate in skeletal tissues.

    PubMed

    Aizenberg, J; Weiner, S; Addadi, L

    2003-01-01

    We describe a new type of composite skeletal tissues in which calcite and stabilized amorphous calcium carbonate (ACC) coexist in well-defined domains. The organisms that form such structures are widely separated in the animal kingdom phylogenetic tree: calcareous sponges and ascidians. This paper compares the microstructures of their composite skeletal elements: The triradiate spicules from the sponge Clathrina are composed of a core of calcite embedded in a thick layer of ACC and covered by a thin calcitic envelope; the tunic spicules from the ascidian Pyura pachydermatina are composed of a core of ACC enveloped by an insoluble organic sheath and covered by a thick calcitic layer. We compare and contrast the macromolecules associated with different amorphous and crystalline phases and their ability to induce the formation of stabilized ACC in vitro.

  18. Giant pop-ins and amorphization in germanium during indentation

    NASA Astrophysics Data System (ADS)

    Oliver, David J.; Bradby, Jodie E.; Williams, Jim S.; Swain, Michael V.; Munroe, Paul

    2007-02-01

    Sudden excursions of unusually large magnitude (>1 μm), "giant pop-ins," have been observed in the force-displacement curve for high load indentation of crystalline germanium (Ge). A range of techniques including Raman microspectroscopy, focused ion-beam cross sectioning, and transmission electron microscopy, are applied to study this phenomenon. Amorphous material is observed in residual indents following the giant pop-in. The giant pop-in is shown to be a material removal event, triggered by the development of shallow lateral cracks adjacent to the indent. Enhanced depth recovery, or "elbowing," observed in the force-displacement curve following the giant pop-in is explained in terms of a compliant response of plates of material around the indent detached by lateral cracking. The possible causes of amorphization are discussed, and the implications in light of earlier indentation studies of Ge are considered.

  19. Growing timescales and lengthscales characterizing vibrations of amorphous solids.

    PubMed

    Berthier, Ludovic; Charbonneau, Patrick; Jin, Yuliang; Parisi, Giorgio; Seoane, Beatriz; Zamponi, Francesco

    2016-07-26

    Low-temperature properties of crystalline solids can be understood using harmonic perturbations around a perfect lattice, as in Debye's theory. Low-temperature properties of amorphous solids, however, strongly depart from such descriptions, displaying enhanced transport, activated slow dynamics across energy barriers, excess vibrational modes with respect to Debye's theory (i.e., a boson peak), and complex irreversible responses to small mechanical deformations. These experimental observations indirectly suggest that the dynamics of amorphous solids becomes anomalous at low temperatures. Here, we present direct numerical evidence that vibrations change nature at a well-defined location deep inside the glass phase of a simple glass former. We provide a real-space description of this transition and of the rapidly growing time- and lengthscales that accompany it. Our results provide the seed for a universal understanding of low-temperature glass anomalies within the theoretical framework of the recently discovered Gardner phase transition.

  20. High Thermal Conductivity of a Hydrogenated Amorphous Silicon Film

    SciTech Connect

    Liu, X.; Feldman, J. L.; Cahill, D. G.; Crandall, R. S.; Bernstein, N.; Photiadis, D. M.; Mehl, M. J.; Papaconstantopoulos, D. A.

    2009-01-23

    We measured the thermal conductivity {kappa} of an 80 {micro}m thick hydrogenated amorphous silicon film prepared by hot-wire chemical-vapor deposition with the 3{omega} (80-300 K) and the time-domain thermoreflectance (300 K) methods. The {kappa} is higher than any of the previous temperature dependent measurements and shows a strong phonon mean free path dependence. We also applied a Kubo based theory using a tight-binding method on three 1000 atom continuous random network models. The theory gives higher {kappa} for more ordered models, but not high enough to explain our results, even after extrapolating to lower frequencies with a Boltzmann approach. Our results show that this material is more ordered than any amorphous silicon previously studied.

  1. Growing timescales and lengthscales characterizing vibrations of amorphous solids.

    PubMed

    Berthier, Ludovic; Charbonneau, Patrick; Jin, Yuliang; Parisi, Giorgio; Seoane, Beatriz; Zamponi, Francesco

    2016-07-26

    Low-temperature properties of crystalline solids can be understood using harmonic perturbations around a perfect lattice, as in Debye's theory. Low-temperature properties of amorphous solids, however, strongly depart from such descriptions, displaying enhanced transport, activated slow dynamics across energy barriers, excess vibrational modes with respect to Debye's theory (i.e., a boson peak), and complex irreversible responses to small mechanical deformations. These experimental observations indirectly suggest that the dynamics of amorphous solids becomes anomalous at low temperatures. Here, we present direct numerical evidence that vibrations change nature at a well-defined location deep inside the glass phase of a simple glass former. We provide a real-space description of this transition and of the rapidly growing time- and lengthscales that accompany it. Our results provide the seed for a universal understanding of low-temperature glass anomalies within the theoretical framework of the recently discovered Gardner phase transition. PMID:27402768

  2. High Thermal Conductivity of a Hydrogenated Amorphous Silicon Film

    NASA Astrophysics Data System (ADS)

    Liu, Xiao; Feldman, J. L.; Cahill, D. G.; Crandall, R. S.; Bernstein, N.; Photiadis, D. M.; Mehl, M. J.; Papaconstantopoulos, D. A.

    2009-01-01

    We measured the thermal conductivity κ of an 80μm thick hydrogenated amorphous silicon film prepared by hot-wire chemical-vapor deposition with the 3ω (80-300 K) and the time-domain thermoreflectance (300 K) methods. The κ is higher than any of the previous temperature dependent measurements and shows a strong phonon mean free path dependence. We also applied a Kubo based theory using a tight-binding method on three 1000 atom continuous random network models. The theory gives higher κ for more ordered models, but not high enough to explain our results, even after extrapolating to lower frequencies with a Boltzmann approach. Our results show that this material is more ordered than any amorphous silicon previously studied.

  3. Spherical silicon photonic microcavities: From amorphous to polycrystalline

    NASA Astrophysics Data System (ADS)

    Fenollosa, R.; Garín, M.; Meseguer, F.

    2016-06-01

    Shaping silicon as a spherical object is not an obvious task, especially when the object size is in the micrometer range. This has the important consequence of transforming bare silicon material in a microcavity, so it is able to confine light efficiently. Here, we have explored the inside volume of such microcavities, both in their amorphous and in their polycrystalline versions. The synthesis method, which is based on chemical vapor deposition, causes amorphous microspheres to have a high content of hydrogen that produces an onionlike distributed porous core when the microspheres are crystallized by a fast annealing regime. This substantially influences the resonant modes. However, a slow crystallization regime does not yield pores, and produces higher-quality-factor resonances that could be fitted to the Mie theory. This allows the establishment of a procedure for obtaining size calibration standards with relative errors of the order of 0.1%.

  4. Nucleation of amorphous shear bands at nanotwins in boron suboxide.

    PubMed

    An, Qi; Reddy, K Madhav; Qian, Jin; Hemker, Kevin J; Chen, Ming-Wei; Goddard, William A

    2016-03-22

    The roles of grain boundaries and twin boundaries in mechanical properties are well understood for metals and alloys. However, for covalent solids, their roles in deformation response to applied stress are not established. Here we characterize the nanotwins in boron suboxide (B6O) with twin boundaries along the {0111} planes using both scanning transmission electron microscopy and quantum mechanics. Then, we use quantum mechanics to determine the deformation mechanism for perfect and twinned B6O crystals for both pure shear and biaxial shear deformations. Quantum mechanics suggests that amorphous bands nucleate preferentially at the twin boundaries in B6O because the twinned structure has a lower maximum shear strength by 7.5% compared with perfect structure. These results, which are supported by experimental observations of the coordinated existence of nanotwins and amorphous shear bands in B6O, provide a plausible atomistic explanation for the influence of nanotwins on the deformation behaviour of superhard ceramics.

  5. Nucleation of amorphous shear bands at nanotwins in boron suboxide

    NASA Astrophysics Data System (ADS)

    An, Qi; Reddy, K. Madhav; Qian, Jin; Hemker, Kevin J.; Chen, Ming-Wei; Goddard, William A., III

    2016-03-01

    The roles of grain boundaries and twin boundaries in mechanical properties are well understood for metals and alloys. However, for covalent solids, their roles in deformation response to applied stress are not established. Here we characterize the nanotwins in boron suboxide (B6O) with twin boundaries along the planes using both scanning transmission electron microscopy and quantum mechanics. Then, we use quantum mechanics to determine the deformation mechanism for perfect and twinned B6O crystals for both pure shear and biaxial shear deformations. Quantum mechanics suggests that amorphous bands nucleate preferentially at the twin boundaries in B6O because the twinned structure has a lower maximum shear strength by 7.5% compared with perfect structure. These results, which are supported by experimental observations of the coordinated existence of nanotwins and amorphous shear bands in B6O, provide a plausible atomistic explanation for the influence of nanotwins on the deformation behaviour of superhard ceramics.

  6. Structural analysis of amorphous phosphates using high performance liquid chromatography

    SciTech Connect

    Sales, B.C.; Boatner, L.A.; Chakoumakos, B.C.; McCallum, J.C.; Ramey, J.O.; Zuhr, R.A.

    1993-12-31

    Determining the atomic-scale structure of amorphous solids has proven to be a formidable scientific and technological problem for the past 100 years. The technique of high-performance liquid chromatography (HPLC) provides unique detailed information regarding the structure of partially disordered or amorphous phosphate solids. Applications of the experimental technique of HPLC to phosphate solids are reviewed, and examples of the type of information that can be obtained with HPLC are presented. Inorganic phosphates encompass a large class of important materials whose applications include: catalysts, ion-exchange media, solid electrolytes for batteries, linear and nonlinear optical components, chelating agents, synthetic replacements for bone and teeth, phosphors, detergents, and fertilizers. Phosphate ions also represent a unique link between living systems and the inorganic world.

  7. Apparatus for production of ultrapure amorphous metals utilizing acoustic cooling

    NASA Technical Reports Server (NTRS)

    Lee, M. C. (Inventor)

    1985-01-01

    Amorphous metals are produced by forming a molten unit of metal and deploying the unit into a bidirectional acoustical levitating field or by dropping the unit through a spheroidizing zone, a slow quenching zone, and a fast quenching zone in which the sphere is rapidly cooled by a bidirectional jet stream created in the standing acoustic wave field produced between a half cylindrical acoustic driver and a focal reflector or a curved driver and a reflector. The cooling rate can be further augmented first by a cryogenic liquid collar and secondly by a cryogenic liquid jacket surrounding a drop tower. The molten unit is quenched to an amorphous solid which can survive impact in a unit collector or is retrieved by a vacuum chuck.

  8. Evolution of Hydrogen Dynamics in Amorphous Ice with Density.

    PubMed

    Parmentier, A; Shephard, J J; Romanelli, G; Senesi, R; Salzmann, C G; Andreani, C

    2015-06-01

    The single-particle dynamics of hydrogen atoms in several of the amorphous ices are reported using a combination of deep inelastic neutron scattering (DINS) and inelastic neutron scattering (INS). The mean kinetic energies of the hydrogen nuclei are found to increase with increasing density, indicating the weakening of hydrogen bonds as well as a trend toward steeper and more harmonic hydrogen vibrational potential energy surfaces. DINS shows much more pronounced changes in the O-H stretching component of the mean kinetic energy going from low- to high-density amorphous ices than indicated by INS and Raman spectroscopy. This highlights the power of the DINS technique to retrieve accurate ground-state kinetic energies beyond the harmonic approximation. In a novel approach, we use information from DINS and INS to determine the anharmonicity constants of the O-H stretching modes. Furthermore, our experimental kinetic energies will serve as important benchmark values for path-integral Monte Carlo simulations.

  9. Atomic Structure of an Amorphous/Crystal Interface

    SciTech Connect

    Shibata, Naoya; Painter, Gayle S; Becher, Paul F; Pennycook, Stephen J

    2006-01-01

    In this study, the authors report atomic-resolution images that illustrate the transition from a crystalline Si{sub 3}N{sub 4} grain across the interface into an amorphous Lu-Si-Mg-N-O glassy phase. The interface is not atomically abrupt, but is comprised of sub-nanometer-scale ordered regions that resemble a LuN-like structure. These ordered clusters bind to the prismatic surface of the Si{sub 3}N{sub 4} grains at specific low energy positions for Lu adsorption as predicted by first-principles calculations. The ordered regions are filamentary in nature, extending for at least two atomic layers into the amorphous pockets at multigrain junctions before disappearing.

  10. Electrochemical degradation of amorphous-silicon photovoltaic modules

    NASA Technical Reports Server (NTRS)

    Mon, G. R.; Ross, R. G., Jr.

    1985-01-01

    Techniques of module electrochemical corrosion research, developed during reliability studies of crystalline-silicon modules (C-Si), have been applied to this new investigation into amorphous-silicon (a-Si) module reliability. Amorphous-Si cells, encapsulated in the polymers polyvinyl butyral (PVB) and ethylene vinyl acetate (EVA), were exposed for more than 1200 hours in a controlled 85 C/85 percent RH environment, with a constant 500 volts applied between the cells and an aluminum frame. Plotting power output reduction versus charge transferred reveals that about 50 percent a-Si cell failures can be expected with the passage of 0.1 to 1.0 Coulomb/cm of cell-frame edge length; this threshold is somewhat less than that determined for C-Si modules.

  11. Occupational exposure to amorphous silica dust and pulmonary function.

    PubMed Central

    Choudat, D; Frisch, C; Barrat, G; el Kholti, A; Conso, F

    1990-01-01

    Respiratory manifestations among 41 workers exposed to amorphous silica dust were compared with a control group comprising 90 workers of equivalent socioeconomic state in the same plant. Flow volumes were determined, blood gas concentrations were measured at rest and during exercise, chest radiographs were obtained, and data about respiratory symptoms were collected by questionnaire. A dust exposure index was calculated for each exposed worker. It was not possible to differentiate between the two groups from the questionnaire, blood gas analysis, or chest radiographs. On the other hand, the tests of respiratory function showed a significant decrease in forced expiratory flow (FEF25-75, FEF50, and FEF75) in the exposed group compared with the controls, although no correlation was found between the exposure index and pulmonary function. It appears that smoking and exposure to amorphous silica synergise to induce small airway disease. PMID:2173947

  12. Gas Atomization of Amorphous Aluminum Powder: Part II. Experimental Investigation

    NASA Astrophysics Data System (ADS)

    Zheng, Baolong; Lin, Yaojun; Zhou, Yizhang; Lavernia, Enrique J.

    2009-12-01

    The optimal processing parameters that are required to atomize amorphous Al were established on the basis of numerical simulations in part I of this study. In this part II, the characterization of cooling rate experienced by gas-atomized, Al-based amorphous powders was studied via experiments. An experimental investigation was implemented to validate the numerical predictions reported in part I of this study. The cooling rate experienced by the powders, for example, was experimentally determined on the basis of dendrite arm spacing correlations, and the results were compared with the numerical predictions. The experimental studies were completed using commercial Al 2024 as a baseline material and Al90Gd7Ni2Fe1 metallic glass (MG). The results showed that the cooling rate of droplets increases with decreasing particle size, with an increasing proportion of helium in the atomization gas and with increasing melt superheat. The experimental results reported in this article suggest good agreement between experiments and numerical simulations.

  13. Controlled Rejuvenation of Amorphous Metals with Thermal Processing

    PubMed Central

    Wakeda, Masato; Saida, Junji; Li, Ju; Ogata, Shigenobu

    2015-01-01

    Rejuvenation is the configurational excitation of amorphous materials and is one of the more promising approaches for improving the deformability of amorphous metals that usually exhibit macroscopic brittle fracture modes. Here, we propose a method to control the level of rejuvenation through systematic thermal processing and clarify the crucial feasibility conditions by means of molecular dynamics simulations of annealing and quenching. We also experimentally demonstrate rejuvenation level control in Zr55Al10Ni5Cu30 bulk metallic glass. Our local heat-treatment recipe (rising temperature above 1.1Tg, followed by a temperature quench rate exceeding the previous) opens avenue to modifying the glass properties after it has been cast and processed into near component shape, where a higher local cooling rate may be afforded by for example transient laser heating, adding spatial control and great flexibility to the processing. PMID:26010470

  14. Breakdown of nonlinear elasticity in amorphous solids at finite temperatures

    NASA Astrophysics Data System (ADS)

    Procaccia, Itamar; Rainone, Corrado; Shor, Carmel A. B. Z.; Singh, Murari

    2016-06-01

    It is known [H. G. E. Hentschel et al., Phys. Rev. E 83, 061101 (2011), 10.1103/PhysRevE.83.061101] that amorphous solids at zero temperature do not possess a nonlinear elasticity theory: besides the shear modulus, which exists, none of the higher order coefficients exist in the thermodynamic limit. Here we show that the same phenomenon persists up to temperatures comparable to that of the glass transition. The zero-temperature mechanism due to the prevalence of dangerous plastic modes of the Hessian matrix is replaced by anomalous stress fluctuations that lead to the divergence of the variances of the higher order elastic coefficients. The conclusion is that in amorphous solids elasticity can never be decoupled from plasticity: the nonlinear response is very substantially plastic.

  15. Anatomy of plastic events in magnetic amorphous solids

    NASA Astrophysics Data System (ADS)

    Hentschel, H. George E.; Procaccia, Itamar; Gupta, Bhaskar Sen

    2016-03-01

    Plastic events in amorphous solids can be much more than just "shear transformation zones" when the positional degrees of freedom are coupled nontrivially to other degrees of freedom. Here we consider magnetic amorphous solids where mechanical and magnetic degrees of freedom interact, leading to rather complex plastic events whose nature must be disentangled. In this paper we uncover the anatomy of the various contributions to some typical plastic events. These plastic events are seen as Barkhausen noise or other "serrated noises." Using theoretical considerations we explain the observed statistics of the various contributions to the considered plastic events. The richness of contributions and their different characteristics imply that in general the statistics of these serrated noises cannot be universal, but rather highly dependent on the state of the system and on its microscopic interactions.

  16. Controlled Rejuvenation of Amorphous Metals with Thermal Processing

    NASA Astrophysics Data System (ADS)

    Wakeda, Masato; Saida, Junji; Li, Ju; Ogata, Shigenobu

    2015-05-01

    Rejuvenation is the configurational excitation of amorphous materials and is one of the more promising approaches for improving the deformability of amorphous metals that usually exhibit macroscopic brittle fracture modes. Here, we propose a method to control the level of rejuvenation through systematic thermal processing and clarify the crucial feasibility conditions by means of molecular dynamics simulations of annealing and quenching. We also experimentally demonstrate rejuvenation level control in Zr55Al10Ni5Cu30 bulk metallic glass. Our local heat-treatment recipe (rising temperature above 1.1Tg, followed by a temperature quench rate exceeding the previous) opens avenue to modifying the glass properties after it has been cast and processed into near component shape, where a higher local cooling rate may be afforded by for example transient laser heating, adding spatial control and great flexibility to the processing.

  17. Multiple routes for vortex depinning in amorphous thin film superconductors

    SciTech Connect

    Groenbech-Jensen, N.; Bishop, A.R.; Dominquez, D.

    1996-07-01

    ffWe present simulations of vortex dynamics in amorphous two-dimensional thin film superconductors, using a new exact method to evaluate long range interactions between vortices. We find that the onset of vortex motion is dominated by filamentary channels of flow. There are multiple patterns of filamentary flow which are stable in a wide range of bias current. As a consequence, there are multiple steps in the differential resistance, each step corresponding to a different pattern of filamentary flow. This results in a strong history dependence of the depinning current and current voltage characteristics. Our results are in agreement with recent experiments on amorphous Mo{sub 77}Ge{sub 23} thin films.

  18. Amorphous ruthenium nanoparticles for enhanced electrochemical water splitting

    NASA Astrophysics Data System (ADS)

    Tee, Si Yin; Lee, Coryl Jing Jun; Safari Dinachali, Saman; Lai, Szu Cheng; Williams, Evan Laurence; Luo, He-Kuan; Chi, Dongzhi; Hor, T. S. Andy; Han, Ming-Yong

    2015-10-01

    This paper demonstrates an optimized fabrication of amorphous Ru nanoparticles through annealing at various temperatures ranging from 150 to 700 °C, which are used as water oxidation catalyst for effective electrochemical water splitting under a low overpotential of less than 300 mV. The amorphous Ru nanoparticles with short-range ordered structure exhibit an optimal and stable electrocatalytic activity after annealing at 250 °C. Interestingly, a small quantity of such Ru nanoparticles in a thin film on fluorine-doped tin oxide glass is also effectively driven by a conventional crystalline silicon solar cell that has excellent capability for harvesting visible light. Remarkably, it achieves an overall solar-to-hydrogen efficiency of 11.3% in acidic electrolyte.

  19. Amorphous ruthenium nanoparticles for enhanced electrochemical water splitting.

    PubMed

    Tee, Si Yin; Lee, Coryl Jing Jun; Dinachali, Saman Safari; Lai, Szu Cheng; Williams, Evan Laurence; Luo, He-Kuan; Chi, Dongzhi; Andy Hor, T S; Han, Ming-Yong

    2015-10-16

    This paper demonstrates an optimized fabrication of amorphous Ru nanoparticles through annealing at various temperatures ranging from 150 to 700 °C, which are used as water oxidation catalyst for effective electrochemical water splitting under a low overpotential of less than 300 mV. The amorphous Ru nanoparticles with short-range ordered structure exhibit an optimal and stable electrocatalytic activity after annealing at 250 °C. Interestingly, a small quantity of such Ru nanoparticles in a thin film on fluorine-doped tin oxide glass is also effectively driven by a conventional crystalline silicon solar cell that has excellent capability for harvesting visible light. Remarkably, it achieves an overall solar-to-hydrogen efficiency of 11.3% in acidic electrolyte. PMID:26404046

  20. Synthesis of amorphous calcium phosphate using various types of cyclodextrins

    SciTech Connect

    Li Yanbao; Wiliana, Tjandra; Tam, Kam C. . E-mail: mkctam@ntu.edu.sg

    2007-05-03

    Amorphous calcium phosphate (ACP) was synthesised in aqueous solution at room temperature using cyclodextrins. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and thermal analysis (DTA/TGA) were performed on the calcium phosphate precipitates obtained from solutions. We observed that only {beta}-CD could stabilise the amorphous phase in the mother solution because of the lower solubility of {beta}-CD in water and the ACP remained stable in aqueous solution for more than 24 h at room temperature. The ACP particle has an initial particle size of less than 40 nm, Ca/P molar ratio of 1.67 and {beta}-CD absorbed on its surface. The mechanism for the stabilisation of ACP is proposed.

  1. Protocol-dependent shear modulus of amorphous solids

    NASA Astrophysics Data System (ADS)

    Nakayama, Daijyu; Yoshino, Hajime; Zamponi, Francesco

    2016-10-01

    We investigate the linear elastic response of amorphous solids to a shear strain at zero temperature. We find that the response is characterized by at least two distinct shear moduli. The first one, {μ\\text{ZFC}} , is associated with the linear response of a single energy minimum. The second, {μ\\text{FC}} , is related to sampling, through plastic events, an ensemble of distinct energy minima. We provide examples of protocols that allow one to measure both shear moduli. In agreement with a theoretical prediction based on the exact solution in infinite spatial dimensions, the ratio {μ\\text{FC}}/{μ\\text{ZFC}} is found to vanish proportionally to the square root of pressure at the jamming transition. Our results establish that amorphous solids are characterized by a rugged energy landscape, which has a deep impact on their elastic response, as suggested by the infinite-dimensional solution.

  2. Nucleation of amorphous shear bands at nanotwins in boron suboxide

    PubMed Central

    An, Qi; Reddy, K. Madhav; Qian, Jin; Hemker, Kevin J.; Chen, Ming-Wei; Goddard III, William A.

    2016-01-01

    The roles of grain boundaries and twin boundaries in mechanical properties are well understood for metals and alloys. However, for covalent solids, their roles in deformation response to applied stress are not established. Here we characterize the nanotwins in boron suboxide (B6O) with twin boundaries along the planes using both scanning transmission electron microscopy and quantum mechanics. Then, we use quantum mechanics to determine the deformation mechanism for perfect and twinned B6O crystals for both pure shear and biaxial shear deformations. Quantum mechanics suggests that amorphous bands nucleate preferentially at the twin boundaries in B6O because the twinned structure has a lower maximum shear strength by 7.5% compared with perfect structure. These results, which are supported by experimental observations of the coordinated existence of nanotwins and amorphous shear bands in B6O, provide a plausible atomistic explanation for the influence of nanotwins on the deformation behaviour of superhard ceramics. PMID:27001922

  3. Deposition of device quality low H content, amorphous silicon films

    DOEpatents

    Mahan, A.H.; Carapella, J.C.; Gallagher, A.C.

    1995-03-14

    A high quality, low hydrogen content, hydrogenated amorphous silicon (a-Si:H) film is deposited by passing a stream of silane gas (SiH{sub 4}) over a high temperature, 2,000 C, tungsten (W) filament in the proximity of a high temperature, 400 C, substrate within a low pressure, 8 mTorr, deposition chamber. The silane gas is decomposed into atomic hydrogen and silicon, which in turn collides preferably not more than 20--30 times before being deposited on the hot substrate. The hydrogenated amorphous silicon films thus produced have only about one atomic percent hydrogen, yet have device quality electrical, chemical, and structural properties, despite this lowered hydrogen content. 7 figs.

  4. Elastic properties of amorphous thin films studied by Rayleigh waves

    SciTech Connect

    Schwarz, R.B.; Rubin, J.B.

    1993-08-01

    Physical vapor deposition in ultra-high vacuum was used to co-deposit nickel and zirconium onto quartz single crystals and grow amorphous Ni{sub 1-x}Zr{sub x} (0.1 < x < 0.87) thin film. A high-resolution surface acoustic wave technique was developed for in situ measurement of film shear moduli. The modulus has narrow maxima at x = 0. 17, 0.22, 0.43, 0.5, 0.63, and 0.72, reflecting short-range ordering and formation of aggregates in amorphous phase. It is proposed that the aggregates correspond to polytetrahedral atom arrangements limited in size by geometrical frustration.

  5. Plasticity of an Amorphous Assembly of Elastic Gel Beads

    NASA Astrophysics Data System (ADS)

    Grosshans, D.; Knaebel, A.; Lequeux, F.

    1995-01-01

    We have studied the rheological properties of an assembly of swollen gel beads in a lack of solvent. The system is an amorphous assembly of packed soft spheres in a given volume. We have studied the plastic behavior of the system, and interpreted it in terms of bead rearrangements within the assembly. Nous avons étudié les propriétés rhéologiques d'un assemblage de billes de gel gonflées en défaut de solvant. Le système est donc une assemblée amorphe de sphères molles écrasées à volume total constant. Nous avons étudié divers aspects du comportement plastique et nous l'avons interprété en termes de réorganisations de billes dans l'assemblage.

  6. Force-field parameters for beryllium complexes in amorphous layers.

    PubMed

    Emelyanova, Svetlana; Chashchikhin, Vladimir; Bagaturyants, Alexander

    2016-09-01

    Unknown force-field parameters for metal organic beryllium complexes used in emitting and electron transporting layers of OLED structures are determined. These parameters can be used for the predictive atomistic simulations of the structure and properties of amorphous organic layers containing beryllium complexes. The parameters are found for the AMBER force field using a relaxed scan procedure and quantum-mechanical DFT calculations of potential energy curves for specific internal (angular) coordinates in a series of three Be complexes (Bebq2; Be(4-mpp)2; Bepp2). The obtained parameters are verified in calculations of some molecular and crystal structures available from either quantum-mechanical DFT calculations or experimental data. Graphical Abstract Beryllium complexes in amorphous layersᅟ.

  7. Physical processes of quartz amorphization due to friction

    NASA Astrophysics Data System (ADS)

    Nakamura, Y.; Muto, J.; Nagahama, H.; Miura, T.; Arakawa, I.; Shimizu, I.

    2011-12-01

    Solid state amorphization of minerals occurs in indentations, in shock experiments, and in high pressure metamorphic quartz rock. A production of amorphous material is also reported in experimentally created silicate gouges (Yund et al., 1990), and in San Andreas Fault core samples (Janssen et al., 2010). Rotary-shear friction experiments of quartz rocks imply dynamic weakening at seismic rates (Di Toro et al., 2004). These experiments have suggested that weakening is caused by formation and thixotropic behavior of a silica gel layer which comprises of very fine particles of hydrated amorphous silica on fault gouges (Goldsby & Tullis, 2002; Hayashi & Tsutsumi, 2010). Therefore, physical processes of amorphization are important to better understand weakening of quartz bearing rocks. In this study, we conducted a pin-on-disk friction experiment to investigate details of quartz amorphization (Muto et al, 2007). Disks were made of single crystals of synthetic and Brazilian quartz. The normal load F and sliding velocity V were ranged from 0.01 N to 1 N and from 0.01 m/s to 2.6 m/s, respectively. The friction was conducted using quartz and diamond pins (curvature radii of 0.2 ~ 3 mm) to large displacements (> 1000 m) under controlled atmosphere. We analyzed experiment samples by Raman spectroscopy and FT-IR. Raman spectroscopy (excitation wavelength 532.1 nm) provides lattice vibration modes, and was used to investigate the degree of amorphization of samples. Raman spectra of friction tracks on the disk show clear bands at wavenumbers of 126, 204, 356, 394, and 464 cm-1, characteristic of intact α-quartz. Remarkably, in experiments using diamond pins (F = 0.8 N, normal stress σr calculated by contact area = 293 ~ 440 MPa, V = 0.12 ~ 0.23 m/s), the bands at 204 and 464 cm-1 gradually broaden to reveal shoulders on the higher-wavenumber sides of these peaks. Especially, two distinguished peaks at 490 and 515 cm-1 and a weak broad peak at 606 cm-1 appear sporadically on

  8. Mechanical anisotropy at the nanoscale in amorphous solids

    SciTech Connect

    Luo, Yun; Li, Qi-Kai; Li, M.

    2015-01-28

    Amorphous solids are randomly disordered without any long-range periodic atomic arrangement and thus appear isotropic. Here, we show in metallic glasses that this view does not hold at small scales: Strong mechanical anisotropy emerges when the sample size decreases below about 15 nm as shown by the marked deviation in stress-strain relations as well as elastic modulus along different loading directions. The size induced mechanical anisotropy is naturally related to structural anisotropy that is absent before loading. The anisotropic stress and modulus versus the size yield different scaling exponents in different stages of deformation, hinting at different deformation mechanisms. The size effect discovered here points to the existence of intrinsic heterogeneity defined by the anisotropy, which may play an important role in structure-property relations in amorphous solids.

  9. The reliability and stability of multijunction amorphous silicon PV modules

    SciTech Connect

    Carlson, D.E.

    1995-11-01

    Solarex is developing a manufacturing process for the commercial production of 8 ft{sup 2} multijunction amorphous silicon (a-Si) PV modules starting in 1996. The device structure used in these multijunction modules is: glass/textured tin oxide/p-i-n/p-i-n/ZnO/Al/EVA/Tedlar where the back junction of the tandem structure contains an amorphous silicon germanium alloy. As an interim step, 4 ft{sup 2} multijunction modules have been fabricated in a pilot production mode over the last several months. The distribution of initial conversion efficiencies for an engineering run of 67 modules (4 ft{sup 2}) is shown. Measurements recently performed at NREL indicate that the actual efficiencies are about 5% higher than those shown, and thus exhibit an average initial conversion efficiency of about 9.5%. The data indicates that the process is relatively robust since there were no modules with initial efficiencies less than 7.5%.

  10. High Resolution Radial Distribution Function of Pure Amorphous Silicon

    SciTech Connect

    Laaziri, K.; Roorda, S.; Chicoine, M.; Kycia, S.; Robertson, J.L.; Wang, J.; Moss, S.C.

    1999-04-01

    The structure factor S(Q) of high purity amorphous Si membranes prepared by ion implantation was measured over an extended Q range (0.03{endash}55 {Angstrom} {sup {minus}1} ). Calculation of the first neighbor shell coordination (C{sub 1} ) as a function of maximum Q indicates that measurement of S(Q) out to at least 40 {Angstrom}{sup {minus}1} is required to reliably determine the radial distribution function (RDF). A 2{percent} change in C{sub 1} and subtle changes in the rest of the RDF were observed upon annealing, consistent with point defect removal. After annealing at 600thinsp{degree}C, C{sub 1}=3.88 , which would explain why amorphous Si is less dense than crystalline Si. {copyright} {ital 1999} {ital The American Physical Society}

  11. Thin film memory matrix using amorphous and high resistive layers

    NASA Technical Reports Server (NTRS)

    Thakoor, Anilkumar P. (Inventor); Lambe, John (Inventor); Moopen, Alexander (Inventor)

    1989-01-01

    Memory cells in a matrix are provided by a thin film of amorphous semiconductor material overlayed by a thin film of resistive material. An array of parallel conductors on one side perpendicular to an array of parallel conductors on the other side enable the amorphous semiconductor material to be switched in addressed areas to be switched from a high resistance state to a low resistance state with a predetermined level of electrical energy applied through selected conductors, and thereafter to be read out with a lower level of electrical energy. Each cell may be fabricated in the channel of an MIS field-effect transistor with a separate common gate over each section to enable the memory matrix to be selectively blanked in sections during storing or reading out of data. This allows for time sharing of addressing circuitry for storing and reading out data in a synaptic network, which may be under control of a microprocessor.

  12. Controlled rejuvenation of amorphous metals with thermal processing.

    PubMed

    Wakeda, Masato; Saida, Junji; Li, Ju; Ogata, Shigenobu

    2015-05-26

    Rejuvenation is the configurational excitation of amorphous materials and is one of the more promising approaches for improving the deformability of amorphous metals that usually exhibit macroscopic brittle fracture modes. Here, we propose a method to control the level of rejuvenation through systematic thermal processing and clarify the crucial feasibility conditions by means of molecular dynamics simulations of annealing and quenching. We also experimentally demonstrate rejuvenation level control in Zr(55)Al(10)Ni(5)Cu(30) bulk metallic glass. Our local heat-treatment recipe (rising temperature above 1.1T(g), followed by a temperature quench rate exceeding the previous) opens avenue to modifying the glass properties after it has been cast and processed into near component shape, where a higher local cooling rate may be afforded by for example transient laser heating, adding spatial control and great flexibility to the processing.

  13. Deposition of device quality low H content, amorphous silicon films

    DOEpatents

    Mahan, Archie H.; Carapella, Jeffrey C.; Gallagher, Alan C.

    1995-01-01

    A high quality, low hydrogen content, hydrogenated amorphous silicon (a-Si:H) film is deposited by passing a stream of silane gas (SiH.sub.4) over a high temperature, 2000.degree. C., tungsten (W) filament in the proximity of a high temperature, 400.degree. C., substrate within a low pressure, 8 mTorr, deposition chamber. The silane gas is decomposed into atomic hydrogen and silicon, which in turn collides preferably not more than 20-30 times before being deposited on the hot substrate. The hydrogenated amorphous silicon films thus produced have only about one atomic percent hydrogen, yet have device quality electrical, chemical, and structural properties, despite this lowered hydrogen content.

  14. Novel method for producing amorphous cellulose only by milling.

    PubMed

    Shimura, Ryoichiro; Nishioka, Akihiro; Kano, Ichiro; Koda, Tomonori; Nishio, Taichi

    2014-02-15

    The present study investigated a novel method for producing amorphous cellulose by milling without adding water. A new type of milling machine was developed (called a shear and cooling milling machine (SCMM)), which was capable of applying mechanical shear and cooling during the milling process. The SCMM consisted of a pair of mortars attached to a servomotor and a ring cooler. Wide-angle X-ray diffraction (WAXD) analysis was used to determine the cellulose crystallinity in samples produced using the SCMM at different milling temperatures. The results of WAXD for cellulose powder milled at lower temperatures exhibited no diffraction peaks. This experimental result demonstrates that the SCMM produces amorphous cellulose easily by cooled milling without the addition of water. The milling conditions, such as the applied shear and cooling, can be used to control the crystallinity of cellulose.

  15. Mechanical strength of amorphous CaCO3 colloidal spheres.

    PubMed

    Faatz, Michael; Cheng, Wei; Wegner, Gerhard; Fytas, George; Penciu, Raluca S; Economou, Eleftherios N

    2005-07-19

    Amorphous glassy CaCO3 colloidal spheres of monomodal size distribution were studied by high-resolution Brillouin light scattering. The Young modulus of 37 GPa and shear modulus of 14 GPa of glassy CaCO3 at a density of 1.9 g/cm3 were extracted from the particle vibration frequencies by employing acoustic wave scattering cross-section calculations. The line shape of the low-frequency modes is a sensitive index of the particle polydispersity.

  16. Charged particle detectors made from thin layers of amorphous silicon

    SciTech Connect

    Morel, J.R.

    1986-05-01

    A series of experiments was conducted to determine the feasibility of using hydrogenated amorphous silicon (..cap alpha..-Si:H) as solid state thin film charged particle detectors. /sup 241/Am alphas were successfully detected with ..cap alpha..-Si:H devices. The measurements and results of these experiments are presented. The problems encountered and changes in the fabrication of the detectors that may improve the performance are discussed.

  17. Magnetostriction measurements of amorphous ribbons and thin films

    NASA Astrophysics Data System (ADS)

    Ouyang, Chien

    The theme of the present work is to measure the saturation magnetostriction constants of amorphous ribbons and thin films. The saturation magnetostriction constants of amorphous ribbons, and thin films of Cosb{39}Nisb{31}Fesb8Sisb8Bsb{14}, CoZrY, and CoZrTb have been measured either by the Small Angle Magnetization Rotation (SAMR) method or by the initial susceptibility method. The SAMR method is used for the soft materials. It is found that the amorphous Cosb{39}Nisb{31}Fesb8Sisb8Bsb{14} prepared by ion beam deposition from an alloy target shows very soft magnetic properties and has a very small negative saturation magnetostriction, lambdasb{s}, of about {-}1×10sp{-7}. Sputtered films of CoZrTb show a strong perpendicular anisotropy when the Tb content is high. We have found that the SAMR method can be applied to CoZrTb films when the Tb content is low. The saturation magnetostriction constant of a sputtered film of Cosb{78.4}Zrsb{20.8}Tbsb{0.8} is 2×10sp{-6}. When the material is not magnetically soft or has a strong perpendicular anisotropy, the initial susceptibility method is used. The saturation magnetostriction constants of amorphous Cosb{77.2}Zrsb{20.4}Tbsb{2.4} and Cosb{72.2}Zrsb{14.6}Ysb{13.2} thin films are 6×10sp{-6}, and (2{˜}6)×10sp{-7}, respectively. The two methods, the SAMR and the initial susceptibility, utilize the same measurement setup making it a very convenient technique which is applicable for a range of materials.

  18. Electrodeposition of amorphous ternary nickel-chromium-phosphorus alloy

    DOEpatents

    Guilinger, Terry R.

    1990-01-01

    Amorphous ternary nickel-chromium-phosphorus alloys are electrodeposited from a bath comprising a nickel salt, a chromium salt, a phosphorus source such as sodium hypophosphite, a complexing agent for the nickel ions, supporting salts to increase conductivity, and a buffering agent. The process is carried out at about room temperature and requires a current density between about 20 to 40 A/dm.sup.2.

  19. Mimas: Preliminary Evidence For Amorphous Water Ice from VIMS

    NASA Technical Reports Server (NTRS)

    Cruikshank, Dale P.; Marzo, G. A.; Pinilla-Alonso, N.; Roush, T. L.; Mastrapa, R. M.; DalleOre, C. M.; Buratti, B. J.; Stephan, K.

    2010-01-01

    We have conducted a statistical clustering analysis (1,2) on a mosaic of VIMS data cubes obtained on February 13, 2010, for Saturn s satellite Mimas. Seven VIMS cubes were geometrically projected and re-sampled to a common spatial resolution. The clustering technique consists of a partitioning algorithm coupled to a criterion that prevents sub-optimal solutions and tests for the influence of random noise in the measurements. The clustering technique is agnostic about the meaning of the clusters, and scientific interpretation requires their a posteriori evaluation. The preliminary results yielded five clusters, demonstrating that spectral variability across Mimas surface is statistically significant. The ratios of the means calculated for each of the clusters show structure within the 1.6- micron water ice band, as well as the shape and the central wavelength of the strong ice band at 2 micron, that map spatially in patterns apparently related to the topography of Mimas, in particular certain regions in and around Herschel crater. The mean spectra of the five clusters, show similarities with laboratory spectra of amorphous and crystalline H2O ice (3) that are suggestive of the presence of an amorphous ice component in certain regions of Mimas, notably on the central peak of Herschel, on the crater floor, and in faults surrounding the crater. This may represent a mixture of both ice phases, or perhaps a layer of amorphous ice on a base of crystalline ice. Another possible occurrence of amorphous ice appears southwest of Herschel, close to the south pole.

  20. Mimas: Preliminary Evidence For Amorphous Water Ice From VIMS

    NASA Astrophysics Data System (ADS)

    Cruikshank, Dale P.; Marzo, G. A.; Pinilla-Alonso, N.; Roush, T. L.; Mastrapa, R. M.; Dalle Ore, C. M.; Buratti, B. J.; Stephan, K.; VIMS Team

    2010-10-01

    We have conducted a statistical clustering analysis (1,2) on a mosaic of VIMS data cubes obtained on February 13, 2010, for Saturn's satellite Mimas. Seven VIMS cubes were geometrically projected and re-sampled to a common spatial resolution. The clustering technique consists of a partitioning algorithm coupled to a criterion that prevents sub-optimal solutions and tests for the influence of random noise in the measurements. The clustering technique is agnostic about the meaning of the clusters, and scientific interpretation requires their a posteriori evaluation. The preliminary results yielded five clusters, demonstrating that spectral variability across Mimas’ surface is statistically significant. The ratios of the means calculated for each of the clusters show structure within the 1.6-µm water ice band, as well as the shape and the central wavelength of the strong ice band at 2 µm that map spatially in patterns apparently related to the topography of Mimas, in particular certain regions in and around Herschel crater. The mean spectra of the five clusters, show similarities with laboratory spectra of amorphous and crystalline H2O ice (3) that are suggestive of the presence of an amorphous ice component in certain regions of Mimas, notably on the central peak of Herschel, on the crater floor, and in faults surrounding the crater. This may represent a mixture of both ice phases, or perhaps a layer of amorphous ice on a base of crystalline ice. Another possible occurrence of amorphous ice appears southwest of Herschel, close to the south pole. 1. Marzo, G. A. et al. J. Geophys. Res. 111, E03002, 2006 2. Marzo, G. A. et al. J. Geophys. Res. 113, E12009, 2008 3. Mastrapa, R. M., et al. Astrophys. J. 701, 1347-1356, 2009

  1. Formation of amorphous metal alloys by chemical vapor deposition

    DOEpatents

    Mullendore, Arthur W.

    1990-01-01

    Amorphous alloys are deposited by a process of thermal dissociation of mixtures or organometallic compounds and metalloid hydrides, e.g., transition metal carbonyl such as nickel carbonyl, and diborane. Various sizes and shapes of deposits can be achieved, including near-net-shape free standing articles, multilayer deposits, and the like. Manipulation or absence of a magnetic field affects the nature and the structure of the deposit.

  2. Formation of amorphous metal alloys by chemical vapor deposition

    DOEpatents

    Mullendore, A.W.

    1988-03-18

    Amorphous alloys are deposited by a process of thermal dissociation of mixtures of organometallic compounds and metalloid hydrides,e.g., transition metal carbonyl, such as nickel carbonyl and diborane. Various sizes and shapes of deposits can be achieved, including near-net-shape free standing articles, multilayer deposits, and the like. Manipulation or absence of a magnetic field affects the nature and the structure of the deposit. 1 fig.

  3. A unified description of crystalline-to-amorphous transitions

    SciTech Connect

    Lam, N.Q.; Okamoto, P.R.; Devanathan, R. |; Meshii, M.

    1993-07-01

    Amorphous metallic alloys can now be synthesized by a variety of solid-state processes demonstrating the need for a more general approach to crystalline-to-amorphous (c-a) transitions. By focusing on static atomic displacements as a measure of chemical and topological disorder, we show that a unified description of c-a transformations can be based on a generalization of the phenomenological melting criterion proposed by Lindemann. The generalized version assumes that melting of a defective crystal occurs whenever the sum of thermal and static mean-square displacements exceeds a critical value identical to that for melting of the defect-free crystal. This implies that chemical or topological disorder measured by static displacements is thermodynamically equivalent to heating, and therefore that the melting temperature of the defective crystal will decrease with increasing amount of disorder. This in turn implies the existence of a critical state of disorder where the melting temperature becomes equal to a glass-transition temperature below which the metastable crystal melts to a glass. The generalized Lindemann melting criterion leads naturally to an interpretation of c-a transformations as defect-induced, low-temperature melting of critically disordered crystals. Confirmation of this criterion is provided by molecular-dynamics simulations of heat-induced melting and of defect-induced amorphization of intermetallic compounds caused either by the production of Frenkel pairs or anti-site defects. The thermodynamic equivalence between static atomic disorder and heating is reflected in the identical softening effects which they have on elastic properties and also in the diffraction analysis of diffuse scattering from disordered crystals, where the effect of static displacements appears as an artificially-enlarged thermal Debye-Waller factor. Predictions of this new, unified approach to melting and amorphization are compared with available experimental information.

  4. Lyophilization monophase solution technique for preparation of amorphous flutamide dispersions.

    PubMed

    Elgindy, Nazik; Elkhodairy, Kadria; Molokhia, Abdallah; Elzoghby, Ahmed

    2011-07-01

    Flutamide (FLT) is a poorly soluble anticancer drug. Therefore, lyophilized dispersions (LDs) of FLT with polyvinylpyrrolidone (PVP) K30, polyethylene glycol (PEG) 6000, and pluronic F127 were prepared via lyophilization monophase solution technique with the aim of increasing its dissolution rate. FLT showed an A(L)-type phase solubility diagrams with PVP and PEG, whereas A(N)-type diagram was obtained with pluronic. The amount of residual tertiary butyl alcohol, determined by gas chromatography, was 0.015-0.021% w/w. Differential scanning calorimetry and X-ray diffractometry revealed that FLT-polymer 1:1 LDs were partially amorphous, whereas the 1:3 and 1:5 LDs were completely amorphous. After 6 months storage, polymers under study inhibited FLT recrystallization maintaining its amorphous form. The particle size of FLT-polymer LDs was between 0.81 and 2.13 μm, with a high surface area (268.43-510.82 m²/g) and porosity (354.01-676.23 e⁻³ mL/g). Also, the poor flow properties of FLT could be improved but to a limited extent. FLT dissolution was significantly enhanced with the fastest dissolution that was achieved using pluronic. After 30 min, about 66.52%, 78.23%, and 81.64% of FLT was dissolved from 1:5 FLT-PVP, PEG, and pluronic LDs, respectively, compared with only 13.45% of FLT. These data suggest that these polymers might be useful adjuncts in preparation and stabilization of amorphous immediate-release FLT LDs.

  5. Neutron scattering from amorphous, disordered and nanocrystalline materials

    SciTech Connect

    Price, D.L.

    1994-10-01

    The author has described the power of neutron diffraction and inelastic scattering techniques for determining the structure and dynamics of disordered systems, using the archetypal glass SiO{sub 2} as a detailed example. Of course the field of amorphous and disordered systems contains a much greater variety of types of materials exhibiting a wide range of possible types of disorder. The author gives a brief review of the varieties of order and disorder exhibited by condensed matter.

  6. Optically induced conductivity changes in amorphous silicon: A historical perspective

    SciTech Connect

    Staebler, D.L.

    1997-07-01

    A historical perspective of the discovery of optically induced changes in amorphous silicon is presented in this paper from my personal point of view. It includes the story of how Chris Wronski and the author discovered the effect, the key elements in the R and D environment that lead to the quick realization that the effect was reversible and reproducible, how the research environment supported the rapid publication of their first paper, and a brief look at the effect from today's perspective.

  7. Characterisation of amorphous and nanocrystalline molecular materials by total scattering

    SciTech Connect

    Billinge, Simon J.L.; Dykhne, Timur; Juhás, Pavol; Boin, Emil; Taylor, Ryan; Florence, Alastair J.; Shankland, Kenneth

    2010-09-17

    The use of high-energy X-ray total scattering coupled with pair distribution function analysis produces unique structural fingerprints from amorphous and nanostructured phases of the pharmaceuticals carbamazepine and indomethacin. The advantages of such facility-based experiments over laboratory-based ones are discussed and the technique is illustrated with the characterisation of a melt-quenched sample of carbamazepine as a nanocrystalline (4.5 nm domain diameter) version of form III.

  8. Detection of charged particles in amorphous silicon layers

    SciTech Connect

    Kaplan, S.N.; Morel, J.R.; Mulera, T.A.; Perez-Mendez, V.; Schnurmacher, G.; Street, R.A.

    1985-10-01

    The successful development of radiation detectors made from amorphous silicon could offer the possibility for relatively easy construction of large area position-sensitive detectors. We have conducted a series of measurements with prototype detectors, on signals derived from alpha particles. The measurement results are compared with simple model calculations, and projections are made of potential applications in high-energy and nuclear physics. 4 refs., 7 figs.

  9. Applications of amorphous track models in radiation biology

    NASA Technical Reports Server (NTRS)

    Cucinotta, F. A.; Nikjoo, H.; Goodhead, D. T.; Wilson, J. W. (Principal Investigator)

    1999-01-01

    The average or amorphous track model uses the response of a system to gamma-rays and the radial distribution of dose about an ion's path to describe survival and other cellular endpoints from proton, heavy ion, and neutron irradiation. This model has been used for over 30 years to successfully fit many radiobiology data sets. We review several extensions of this approach that address objections to the original model, and consider applications of interest in radiobiology and space radiation risk assessment. In the light of present views of important cellular targets, the role of target size as manifested through the relative contributions from ion-kill (intra-track) and gamma-kill (inter-track) remains a critical question in understanding the success of the amorphous track model. Several variations of the amorphous model are discussed, including ones that consider the radial distribution of event-sizes rather than average electron dose, damage clusters rather than multiple targets, and a role for repair or damage processing.

  10. Developments in the Ni-Nb-Zr amorphous alloy membranes

    NASA Astrophysics Data System (ADS)

    Sarker, S.; Chandra, D.; Hirscher, M.; Dolan, M.; Isheim, D.; Wermer, J.; Viano, D.; Baricco, M.; Udovic, T. J.; Grant, D.; Palumbo, O.; Paolone, A.; Cantelli, R.

    2016-03-01

    Most of the global H2 production is derived from hydrocarbon-based fuels, and efficient H2/CO2 separation is necessary to deliver a high-purity H2 product. Hydrogen-selective alloy membranes are emerging as a viable alternative to traditional pressure swing adsorption processes as a means for H2/CO2 separation. These membranes can be formed from a wide range of alloys, and those based on Pd are the closest to commercial deployment. The high cost of Pd (USD ~31,000 kg-1) is driving the development of less-expensive alternatives, including inexpensive amorphous (Ni60Nb40)100- x Zr x alloys. Amorphous alloy membranes can be fabricated directly from the molten state into continuous ribbons via melt spinning and depending on the composition can exhibit relatively high hydrogen permeability between 473 and 673 K. Here we review recent developments in these low-cost membrane materials, especially with respect to permeation behavior, electrical transport properties, and understanding of local atomic order. To further understand the nature of these solids, atom probe tomography has been performed, revealing amorphous Nb-rich and Zr-rich clusters embedded in majority Ni matrix whose compositions deviated from the nominal overall composition of the membrane.

  11. Pressure-induced amorphization and orientational disorder in potash alum

    NASA Astrophysics Data System (ADS)

    Sakuntala, T.; Arora, Akhilesh K.; Shekar, N. V. Chandra; Sahu, P. Ch

    2000-05-01

    Pressure-induced amorphization in potassium aluminium sulphate dodecahydrate (potash alum) has been studied using Raman spectroscopy in a diamond anvil cell up to a pressure of 15 GPa. In potash alum, some of the sulphate ions are misoriented with their S-O bond pointing towards potassium rather than aluminium, leading to an `orientational disorder' which ranges from 10 to 24% at ambient conditions. The disorder is quantified from the intensities of the Raman lines characteristic of the two orientations. The samples with low initial disorder exhibit a sequence of two structural phase transitions occurring at 1.5 and 9 GPa respectively. The phase above 1.5 GPa, which could be pressure quenched to ambient conditions, is found to be free from orientational disorder. On the other hand, in the samples with high initial disorder, the disorder is found to grow as a function of pressure and beyond a critical value the system turns amorphous, which is confirmed from the disappearance of sharp diffraction peaks. In view of these results it is apparent that the orientational disorder is the driving mechanism of amorphization in potash alum. The different initial disorders in different samples are believed to arise from a combination of a dynamic disorder (equilibrium) and a static disorder arising from the defects. This defect could possibly be a missing molecule in the water octahedra around the potassium ion.

  12. Laterally inherently thin amorphous-crystalline silicon heterojunction photovoltaic cell

    SciTech Connect

    Chowdhury, Zahidur R. Kherani, Nazir P.

    2014-12-29

    This article reports on an amorphous-crystalline silicon heterojunction photovoltaic cell concept wherein the heterojunction regions are laterally narrow and distributed amidst a backdrop of well-passivated crystalline silicon surface. The localized amorphous-crystalline silicon heterojunctions consisting of the laterally thin emitter and back-surface field regions are precisely aligned under the metal grid-lines and bus-bars while the remaining crystalline silicon surface is passivated using the recently proposed facile grown native oxide–plasma enhanced chemical vapour deposited silicon nitride passivation scheme. The proposed cell concept mitigates parasitic optical absorption losses by relegating amorphous silicon to beneath the shadowed metallized regions and by using optically transparent passivation layer. A photovoltaic conversion efficiency of 13.6% is obtained for an untextured proof-of-concept cell illuminated under AM 1.5 global spectrum; the specific cell performance parameters are V{sub OC} of 666 mV, J{sub SC} of 29.5 mA-cm{sup −2}, and fill-factor of 69.3%. Reduced parasitic absorption, predominantly in the shorter wavelength range, is confirmed with external quantum efficiency measurement.

  13. Dynamic relaxation of a liquid cavity under amorphous boundary conditions.

    PubMed

    Cavagna, Andrea; Grigera, Tomás S; Verrocchio, Paolo

    2012-05-28

    The growth of cooperatively rearranging regions was invoked long ago by Adam and Gibbs to explain the slowing down of glass-forming liquids. The lack of knowledge about the nature of the growing order, though, complicates the definition of an appropriate correlation function. One option is the point-to-set (PTS) correlation function, which measures the spatial span of the influence of amorphous boundary conditions on a confined system. By using a swap Monte Carlo algorithm we measure the equilibration time of a liquid droplet bounded by amorphous boundary conditions in a model glass-former at low temperature, and we show that the cavity relaxation time increases with the size of the droplet, saturating to the bulk value when the droplet outgrows the point-to-set correlation length. This fact supports the idea that the point-to-set correlation length is the natural size of the cooperatively rearranging regions. On the other hand, the cavity relaxation time computed by a standard, nonswap dynamics, has the opposite behavior, showing a very steep increase when the cavity size is decreased. We try to reconcile this difference by discussing the possible hybridization between mode-coupling theory and activated processes, and by introducing a new kind of amorphous boundary conditions, inspired by the concept of frozen external state as an alternative to the commonly used frozen external configuration. PMID:22667566

  14. Molecular dynamics simulations of nanometric cutting mechanisms of amorphous alloy

    NASA Astrophysics Data System (ADS)

    Zhu, Peng-Zhe; Qiu, Chen; Fang, Feng-Zhou; Yuan, Dan-Dan; Shen, Xue-Cen

    2014-10-01

    Molecular dynamics simulations are employed to study the nanometric cutting process of Cu50Zr50 amorphous alloy. The effects of cutting depth, cutting speed and tool edge radius on the cutting force, workpiece pile-up and temperature of the cutting region are studied to investigate the mechanisms of the material removal and surface formation in the nanometric cutting process. It is found that the material removal of amorphous alloy workpiece is mainly based on extrusion at the nanoscale instead of shearing at the macroscale. The plastic deformation of amorphous alloy is mainly due to the formation of shear transformation zones during the nanometric cutting process. The results also suggest that bigger cutting depth and cutting speed will lead to larger tangential force and normal force. However, the tool edge radius has a negligible effect on the tangential force although the normal force increases with the increase of tool edge radius. The workpiece pile-up increases with an increase of the cutting depth, but decreases with an increase of the edge radius of the tool. The workpiece pile-up is not significantly affected by the cutting speed. It is also found that larger cutting depth and cutting speed will result in higher temperature in the cutting region of workpiece and the average Newtonian layer temperature of the tool. Tool edge radius has no significant effect on the temperature distribution of the workpiece and the average Newtonian layer temperature of the tool.

  15. Physiologically Based Absorption Modeling for Amorphous Solid Dispersion Formulations.

    PubMed

    Mitra, Amitava; Zhu, Wei; Kesisoglou, Filippos

    2016-09-01

    Amorphous solid dispersion (ASD) formulations are routinely used to enable the delivery of poorly soluble compounds. This type of formulations can enhance bioavailability due to higher kinetic solubility of the drug substance and increased dissolution rate of the formulation, by the virtue of the fact that the drug molecule exists in the formulation in a high energy amorphous state. In this article we report the application of physiologically based absorption models to mechanistically understand the clinical pharmacokinetics of solid dispersion formulations. Three case studies are shown here to cover a wide range of ASD bioperformance in human and modeling to retrospectively understand their in vivo behavior. Case study 1 is an example of fairly linear PK observed with dose escalation and the use of amorphous solubility to predict bioperformance. Case study 2 demonstrates the development of a model that was able to accurately predict the decrease in fraction absorbed (%Fa) with dose escalation thus demonstrating that such model can be used to predict the clinical bioperformance in the scenario where saturation of absorption is observed. Finally, case study 3 shows the development of an absorption model with the intent to describe the observed incomplete and low absorption in clinic with dose escalation. These case studies highlight the utility of physiologically based absorption modeling in gaining a thorough understanding of ASD performance and the critical factors impacting performance to drive design of a robust drug product that would deliver the optimal benefit to the patients. PMID:27442959

  16. Formulation design and evaluation of amorphous ABT-102 nanoparticles.

    PubMed

    Jog, Rajan; Kumar, Sumit; Shen, Jie; Jugade, Nital; Tan, David Cheng Thiam; Gokhale, Rajeev; Burgess, Diane J

    2016-02-10

    Amorphous nanoparticles are able to enhance the kinetic solubility and concomitant dissolution rates of BCS class II and BCS class II/IV molecules due to their characteristic increased supersaturation levels, smaller particle size and greater surface area. A DoE approach was applied to investigate formulation and spray drying process parameters for the preparation of spray dried amorphous ABT-102 nanoparticles. Stability studies were performed on the optimized formulations to monitor physical and chemical changes under different temperature and humidity conditions. SLS/soluplus and SLS/PVP K25 were the best stabilizer combinations. Trehalose was used to prevent nanoparticle aggregation during spray drying. Particle size distribution, moisture content, PXRD, PLM, FTIR and in vitro dissolution were utilized to characterize the spray dried nanoparticle formulations. The formulations prepared using soluplus showed enhanced dissolution rate compared to those prepared using PVP K25. Following three months storage, it was observed that the formulations stored at 4°C were stable in terms of particle size distribution, moisture content, and crystallinity, whereas those stored at 25°C/60%RH and 40°C/75%RH were unstable. A predictive model to prepare stable solid spray dried amorphous ABT-102 nanoparticles, incorporating both formulation and process parameters, was successfully developed using multiple linear regression analysis. PMID:26705150

  17. Electrical characteristics of amorphous molybdenum-nickel contacts to silicon

    NASA Technical Reports Server (NTRS)

    Kung, K. T.-Y.; Nicolet, M.-A.; Suni, I.

    1984-01-01

    The electrical characteristics of sputtered, amorphous Mo-Ni contacts have been measured on both p- and n-type Si, as functions of composition (30, 54, and 58 at. percent Mo). The contact resistivity on both p(+) and n(+) Si is in the 0.00000 ohm sq cm range. The barrier height for as-deposited samples varies between phi-bp = 0.47-0.42 V on p-type Si and between phi-bn = 0.63-0.68 V on n-type Si, as the composition of the amorphous layer goes from Ni-rich to Mo-rich. The sum phi-bp + phi-bn always equals 1.12 V, within experimental error. After thermal treatment at 500 C for 1/2 h, the contact resistivity changes by a factor of two or less, while the barrier height changes by at most approximately 0.05 V. In light of these results, the amorphous Mo-Ni film makes good ohmic contacts to silicon.

  18. Molecular structure of vapor-deposited amorphous selenium

    NASA Astrophysics Data System (ADS)

    Goldan, A. H.; Li, C.; Pennycook, S. J.; Schneider, J.; Blom, A.; Zhao, W.

    2016-10-01

    The structure of amorphous selenium is clouded with much uncertainty and contradictory results regarding the dominance of polymeric chains versus monomer rings. The analysis of the diffraction radial distribution functions are inconclusive because of the similarities between the crystalline allotropes of selenium in terms of the coordination number, bond length, bond angle, and dihedral angle. Here, we took a much different approach and probed the molecular symmetry of the thermodynamically unstable amorphous state via analysis of structural phase transformations. We verified the structure of the converted metastable and stable crystalline structures using scanning transmission electron microscopy. In addition, given that no experimental technique can tell us the exact three-dimensional atomic arrangements in glassy semiconductors, we performed molecular-dynamic simulations using a well-established empirical three-body interatomic potential. We developed a true vapor-deposited process for the deposition of selenium molecules onto a substrate using empirical molecular vapor compositions and densities. We prepared both vapor-deposited and melt-quenched samples and showed that the simulated radial distribution functions match very well to experiment. The combination of our experimental and molecular-dynamic analyses shows that the structures of vapor- and melt-quenched glassy/amorphous selenium are quite different, based primarily on rings and chains, respectively, reflecting the predominant structure of the parent phase in its thermodynamic equilibrium.

  19. Enhanced Multiple Exciton Generation in Amorphous Silicon Nanoparticles

    NASA Astrophysics Data System (ADS)

    Kryjevski, Andrei; Mihaylov, Deyan; Kilin, Dmitri

    2015-03-01

    Multiple exciton generation (MEG) in nm-sized hydrogen-passivated silicon nanowires (NWs), and quasi two-dimensional nanofilms depends strongly on the degree of the core structural disorder as shown by the many-body perturbation theory (MBPT) calculations based on the DFT simulations. Here, we use the HSE exchange correlation functional. In MBPT, we work to the 2nd order in the electron-photon coupling and in the approximate screened Coulomb interaction. We also include the effect of excitons for which we solve Bethe-Salpeter Equation. We calculate quantum efficiency (QE), the average number of excitons created by a single absorbed photon, in 3D arrays of Si29H36 quantum dots, NWs, and quasi 2D silicon nanofilms, all with both crystalline and amorphous core structures. Efficient MEG with QE of 1.3 up to 1.8 at the photon energy of about 3Eg , where Eg is the gap, is predicted in these nanoparticles except for the crystalline NW and film where QE ~= 1 . MEG in the amorphous nanoparticles is enhanced by the electron localization due to structural disorder. The exciton effects significantly red-shift QE (Ephoton) curves. Nanometer-sized amorphous silicon NWs and films are predicted to have effective MEG within the solar spectrum range. We acknowledge NSF support (CHE-1413614) for method development.

  20. Characterization of photonic amorphous structures with different characteristic lengths

    NASA Astrophysics Data System (ADS)

    Wen, Cheng-Chi; Hung, Yu-Chueh

    2016-04-01

    Photonic amorphous structure (PAS) has attracted increasing research attention due to their interesting characteristics, such as noniridescent structural colors and isotropic photonic band gap. In this work, we present PAS with different characteristic lengths and analyze their structural and topological properties. First, a Fourier spectral method was used to solve Cahn-Hilliard equation and generate a spinodal binary phase structure. By changing the time of the evolution of phase field, mobility, and standard deviation, the characteristic length of amorphous structures can be adjusted. We present the numerical analysis based on finite-difference time-domain (FDTD) method to characterize the density of state (DOS) of PAS based on different time of the evolution of phase field. The corresponding spatial Fourier spectrum of PAS is calculated to examine the characteristic length, and the photonic band gap properties will be discussed in association with the characteristic length. These results are crucial for design of new optical materials display devices base on dielectric amorphous photonic structures.

  1. Stabilization of the Amorphous Ezetimibe Drug by Confining Its Dimension.

    PubMed

    Knapik, J; Wojnarowska, Z; Grzybowska, K; Jurkiewicz, K; Stankiewicz, A; Paluch, M

    2016-04-01

    The purpose of this paper is to investigate the influence of nanoconfinement on the molecular mobility, as well as on the physical stability, of amorphous ezetimibe drug. Two guest/host systems, ezetimibe-Aeroperl 300 and ezetimibe-Neusilin US2, were prepared and studied using various experimental techniques, such as X-ray diffraction (XRD), differential scanning calorimetry (DSC), and broadband dielectric spectroscopy (BDS). Our investigation has shown that the molecular mobility of the examined anticholesterol agent incorporated into nanopore matrices strongly depends on the pore size of the host system. Moreover, it was found that the amorphous ezetimibe confined in 30 nm pores of Aeroperl 300 has a tendency to recrystallize, while the drug incorporated into the smaller--5 nm--pores of Neusilin US2 is not able to crystallize. It has been shown that this significant stabilization of ezetimibe drug can be achieved by an interplay of three factors: changes in molecular dynamics of the confined amorphous drug, the immobilization effect of pore walls on a part of ezetimibe molecules, and the use of host materials with pores that are smaller than the critical size of the drug crystal nuclei. PMID:26981876

  2. Amorphous azithromycin with improved aqueous solubility and intestinal membrane permeability.

    PubMed

    Aucamp, Marique; Odendaal, Roelf; Liebenberg, Wilna; Hamman, Josias

    2015-01-01

    Azithromycin (AZM) is a poorly soluble macrolide antibacterial agent. Its low solubility is considered as the major contributing factor to its relatively low oral bioavailability. The aim of this study was to improve the solubility of this active pharmaceutical ingredient (API) by preparing an amorphous form by quench cooling of the melt and to study the influence of the improved solubility on membrane permeability. The amorphous azithromycin (AZM-A) exhibited a significant increase in water solubility when compared to the crystalline azithromycin dihydrate (AZM-DH). The influence that the improved solubility could have on membrane permeability was also studied. The apparent permeability coefficient (Papp) values of AZM-A were statistically significantly higher (p < 0.05) than crystalline AZM-DH at pH values of 6.8 and 7.2. The results therefore indicated that the improved solubility of AZM in the amorphous form also produced improved permeability across excised intestinal tissue at physiological pH values found in the small intestine.

  3. Magnetoimpedance of cobalt-based amorphous ribbons/polymer composites

    NASA Astrophysics Data System (ADS)

    Semirov, A. V.; Derevyanko, M. S.; Bukreev, D. A.; Moiseev, A. A.; Kudryavtsev, V. O.; Safronov, A. P.

    2016-10-01

    The combined influence of the temperature, the elastic tensile stress and the external magnetic field on the total impedance and impedance components were studied for rapidly quenched amorphous Co75Fe5Si4B16 ribbons. Both as-cast amorphous ribbons and Co75Fe5Si4B16/polymer amorphous ribbon based composites were considered. Following polymer coverings were studied: modified rubber solution in o-xylene, solution of butyl methacrylate and methacrylic acid copolymer in isopropanol and solution of polymethylphenylsiloxane resin in toluene. All selected composites showed very good adhesion of the coverings and allowed to provide temperature measurements from 163 K up to 383 K under the applied deforming tensile force up to 30 N. The dependence of the modulus of the impedance and its components on the external magnetic field was influenced by the elastic tensile stresses and was affected by the temperature of the samples. It was shown that maximal sensitivity of the impedance and its components to the external magnetic field was observed at minimal temperature and maximal deforming force depended on the frequency of an alternating current.

  4. Deep electron and hole polarons and bipolarons in amorphous oxide

    NASA Astrophysics Data System (ADS)

    Kaviani, Moloud; Strand, Jack; Afanas'ev, Valery V.; Shluger, Alexander L.

    2016-07-01

    Amorphous (a)-HfO2 is a prototype high dielectric constant insulator with wide technological applications. Using ab initio calculations we show that excess electrons and holes can trap in a-HfO2 in energetically much deeper polaron states than in the crystalline monoclinic phase. The electrons and holes localize at precursor sites, such as elongated Hf-O bonds or undercoordinated Hf and O atoms, and the polaronic relaxation is amplified by the local disorder of amorphous network. Single electron polarons produce states in the gap at ˜2 eV below the bottom of the conduction band with average trapping energies of 1.0 eV. Two electrons can form even deeper bipolaron states on the same site. Holes are typically localized on undercoordinated O ions with average trapping energies of 1.4 eV. These results advance our general understanding of charge trapping in amorphous oxides by demonstrating that deep polaron states are inherent and do not require any bond rupture to form precursor sites.

  5. Hole conduction pathways in transparent amorphous tin oxides

    NASA Astrophysics Data System (ADS)

    Wahila, Matthew; Lebens-Higgins, Zachary; Quackenbush, Nicholas; Piper, Louis; Butler, Keith; Hendon, Christopher; Walsh, Aron; Watson, Graeme

    P-type transparent amorphous oxide semiconductors (TAOS) have yet to be sufficiently demonstrated or commercialized, severely limiting the possible device architecture of transparent and flexible oxide electronics. The lack of p-type amorphous oxide candidates mainly originates from the directional oxygen 2 p character of their topmost valence states. Previous attempts to create p-type oxides have involved hybridization of the O 2 p with metal orbitals, such as with CuAlO2 and its Cu 3 d - O 2 p hybridization. However, the highly directional nature of the utilized orbitals means that structural disorder inhibits hybridization and severely disrupts hole-conduction pathways. Crystalline stannous oxide (SnO) and other lone-pair active post-transition metal oxides can have reduced localization at the valence band edge due to complex hybridization between the O 2 p, metal p, and spherical metal s-orbitals. I will discuss our investigation of structural disorder in SnO. Using a combination of synchrotron spectroscopy, and atomistic calculations, our investigation elucidates the important interplay between atomistic and electronic structure in establishing continuous hole conduction pathways at the valence band edge of transparent amorphous oxides.

  6. Laterally inherently thin amorphous-crystalline silicon heterojunction photovoltaic cell

    NASA Astrophysics Data System (ADS)

    Chowdhury, Zahidur R.; Kherani, Nazir P.

    2014-12-01

    This article reports on an amorphous-crystalline silicon heterojunction photovoltaic cell concept wherein the heterojunction regions are laterally narrow and distributed amidst a backdrop of well-passivated crystalline silicon surface. The localized amorphous-crystalline silicon heterojunctions consisting of the laterally thin emitter and back-surface field regions are precisely aligned under the metal grid-lines and bus-bars while the remaining crystalline silicon surface is passivated using the recently proposed facile grown native oxide-plasma enhanced chemical vapour deposited silicon nitride passivation scheme. The proposed cell concept mitigates parasitic optical absorption losses by relegating amorphous silicon to beneath the shadowed metallized regions and by using optically transparent passivation layer. A photovoltaic conversion efficiency of 13.6% is obtained for an untextured proof-of-concept cell illuminated under AM 1.5 global spectrum; the specific cell performance parameters are VOC of 666 mV, JSC of 29.5 mA-cm-2, and fill-factor of 69.3%. Reduced parasitic absorption, predominantly in the shorter wavelength range, is confirmed with external quantum efficiency measurement.

  7. Investigation of limit state criteria for amorphous metals

    NASA Astrophysics Data System (ADS)

    Comanici, A. M.; Sandovici, A.; Barsanescu, P. D.

    2016-08-01

    The name of amorphous metals is assigned to metals that have a non-crystalline structure, but they are also very similar to glass if we look into their properties. A very distinguished feature is the fact that amorphous metals, also known as metallic glasses, show a good electrical conductivity. The extension of the limit state criteria for different materials makes this type of alloy a choice to validate the new criterions. Using a new criterion developed for biaxial and triaxial state of stress, the results are investigated in order to determine the applicability of the mathematical model for these amorphous metals. Especially for brittle materials, it is extremely important to find suitable fracture criterion. Mohr-Coulomb criterion, which is permitting a linear failure envelope, is often used for very brittle materials. But for metallic glasses this criterion is not consistent with the experimental determinations. For metallic glasses, and other high-strength materials, Rui Tao Qu and Zhe Feng Zhang proposed a failure envelope modeling with an ellipse in σ-τ coordinates. In this paper this model is being developed for principal stresses space. It is also proposed a method for transforming σ-τ coordinates in principal stresses coordinates and the theoretical results are consistent with the experimental ones.

  8. Sub-amorphous thermal conductivity in ultrathin crystalline silicon nanotubes.

    PubMed

    Wingert, Matthew C; Kwon, Soonshin; Hu, Ming; Poulikakos, Dimos; Xiang, Jie; Chen, Renkun

    2015-04-01

    Thermal transport behavior in nanostructures has become increasingly important for understanding and designing next generation electronic and energy devices. This has fueled vibrant research targeting both the causes and ability to induce extraordinary reductions of thermal conductivity in crystalline materials, which has predominantly been achieved by understanding that the phonon mean free path (MFP) is limited by the characteristic size of crystalline nanostructures, known as the boundary scattering or Casimir limit. Herein, by using a highly sensitive measurement system, we show that crystalline Si (c-Si) nanotubes (NTs) with shell thickness as thin as ∼5 nm exhibit a low thermal conductivity of ∼1.1 W m(-1) K(-1). Importantly, this value is lower than the apparent boundary scattering limit and is even about 30% lower than the measured value for amorphous Si (a-Si) NTs with similar geometries. This finding diverges from the prevailing general notion that amorphous materials represent the lower limit of thermal transport but can be explained by the strong elastic softening effect observed in the c-Si NTs, measured as a 6-fold reduction in Young's modulus compared to bulk Si and nearly half that of the a-Si NTs. These results illustrate the potent prospect of employing the elastic softening effect to engineer lower than amorphous, or subamorphous, thermal conductivity in ultrathin crystalline nanostructures.

  9. TOXICITY OF AMORPHOUS SILICA NANOPARTICLES IN MOUSE KERATINOCYTES

    SciTech Connect

    Yu, Kyung; Wang, Wei; Gu, Baohua; Hussain, Saber

    2009-01-01

    The present study was designed to examine the uptake, localization and the cytotoxic effects of well-dispersed amorphous silica nanoparticles in mouse keratinocytes (HEL-30). Mouse keratinocytes were exposed for 24h to various concentrations of amorphous silica nanoparticles in homogeneous suspensions of average size distribution (30, 48, 118 and 535 nm SiO2) then assessed for uptake and biochemical changes. Results of transmission electron microscopy revealed all sizes of silica were taken up into the cells and localized into the cytoplasm. The lactate dehydrogenase (LDH) assay shows LDH leakage was dose- and size-dependent with exposure to 30 and 48 nm nanoparticles. However, no LDH leakage was observed for either 118 or 535 nm nanoparticles. The mitochondrial viability assay (MTT) showed significant toxicity for 30 and 48 nm at high concentrations (100 g/mL) compare to the 118 and 535 nm particles. Further studies were carried out to investigate if cellular reduced GSH and mitochondria membrane potential are involved in the mechanism of SiO2 toxicity. The redox potential of cells (GSH) was reduced significantly at concentrations of 50, 100 and 200 g/mL at 30 nm nanoparticle exposures. However, silica nanoparticles larger than 30 nm showed no changes in GSH levels. Reactive oxygen species (ROS) formation did not show any significant change between controls and the exposed cells. In summary, amorphous silica nanoparticles below 100 nm induced cytotoxicity suggest size-of the particles is critical to produce biological effects.

  10. Hardness and microplasticity of nanocrystalline and amorphous calcium phosphate coatings

    NASA Astrophysics Data System (ADS)

    Ievlev, V. M.; Kostyuchenko, A. V.; Darinskii, B. M.; Barinov, S. M.

    2014-02-01

    The hardness of thin (1.0-4.0 μm) hydroxyapatite coatings with different structures (nanocrystalline, amorphous-crystalline, and amorphous) grown by rf magnetron sputtering on Ti and Si plates has been studied using the nanoindentation method. All the grown structures are characterized by the strain which has reversible and irreversible components. The hardness of nanocrystalline coatings (about 10 GPa) corresponds to the average hardness of hydroxyapatite single crystals. The structure of nanocrystalline coatings in the indentation zone and outside it has been investigated and changes in the structure under the indenter have been revealed using high-resolution transmission electron microscopy. From a comparison of the hardnesses of coatings with different structures and based on an analysis of the intragranular structure, it has been assumed that the plastic deformation occurs according to a dislocation-free mechanism. The plastic deformation is interpreted in terms of the cluster representation of the hydroxyapatite structure and amorphous calcium phosphates of the same elemental composition and cluster-boundary sliding during the deformation.

  11. Stochastic approach to plasticity and yield in amorphous solids

    NASA Astrophysics Data System (ADS)

    Hentschel, H. G. E.; Jaiswal, Prabhat K.; Procaccia, Itamar; Sastry, Srikanth

    2015-12-01

    We focus on the probability distribution function (PDF) P (Δ γ ;γ ) where Δ γ are the measured strain intervals between plastic events in a athermal strained amorphous solids, and γ measures the accumulated strain. The tail of this distribution as Δ γ →0 (in the thermodynamic limit) scales like Δ γη . The exponent η is related via scaling relations to the tail of the PDF of the eigenvalues of the plastic modes of the Hessian matrix P (λ ) which scales like λθ, η =(θ -1 )/2 . The numerical values of η or θ can be determined easily in the unstrained material and in the yielded state of plastic flow. Special care is called for in the determination of these exponents between these states as γ increases. Determining the γ dependence of the PDF P (Δ γ ;γ ) can shed important light on plasticity and yield. We conclude that the PDF's of both Δ γ and λ are not continuous functions of γ . In slowly quenched amorphous solids they undergo two discontinuous transitions, first at γ =0+ and then at the yield point γ =γ Y to plastic flow. In quickly quenched amorphous solids the second transition is smeared out due to the nonexisting stress peak before yield. The nature of these transitions and scaling relations with the system size dependence of <Δ γ > are discussed.

  12. Stochastic approach to plasticity and yield in amorphous solids.

    PubMed

    Hentschel, H G E; Jaiswal, Prabhat K; Procaccia, Itamar; Sastry, Srikanth

    2015-12-01

    We focus on the probability distribution function (PDF) P(Δγ;γ) where Δγ are the measured strain intervals between plastic events in a athermal strained amorphous solids, and γ measures the accumulated strain. The tail of this distribution as Δγ→0 (in the thermodynamic limit) scales like Δγ(η). The exponent η is related via scaling relations to the tail of the PDF of the eigenvalues of the plastic modes of the Hessian matrix P(λ) which scales like λ(θ), η=(θ-1)/2. The numerical values of η or θ can be determined easily in the unstrained material and in the yielded state of plastic flow. Special care is called for in the determination of these exponents between these states as γ increases. Determining the γ dependence of the PDF P(Δγ;γ) can shed important light on plasticity and yield. We conclude that the PDF's of both Δγ and λ are not continuous functions of γ. In slowly quenched amorphous solids they undergo two discontinuous transitions, first at γ=0(+) and then at the yield point γ=γ(Y) to plastic flow. In quickly quenched amorphous solids the second transition is smeared out due to the nonexisting stress peak before yield. The nature of these transitions and scaling relations with the system size dependence of 〈Δγ〉 are discussed.

  13. Viscous friction between crystalline and amorphous phase of dragline silk.

    PubMed

    Patil, Sandeep P; Xiao, Senbo; Gkagkas, Konstantinos; Markert, Bernd; Gräter, Frauke

    2014-01-01

    The hierarchical structure of spider dragline silk is composed of two major constituents, the amorphous phase and crystalline units, and its mechanical response has been attributed to these prime constituents. Silk mechanics, however, might also be influenced by the resistance against sliding of these two phases relative to each other under load. We here used atomistic molecular dynamics (MD) simulations to obtain friction forces for the relative sliding of the amorphous phase and crystalline units of Araneus diadematus spider silk. We computed the coefficient of viscosity of this interface to be in the order of 10(2) Ns/m(2) by extrapolating our simulation data to the viscous limit. Interestingly, this value is two orders of magnitude smaller than the coefficient of viscosity within the amorphous phase. This suggests that sliding along a planar and homogeneous surface of straight polyalanine chains is much less hindered than within entangled disordered chains. Finally, in a simple finite element model, which is based on parameters determined from MD simulations including the newly deduced coefficient of viscosity, we assessed the frictional behavior between these two components for the experimental range of relative pulling velocities. We found that a perfectly relative horizontal motion has no significant resistance against sliding, however, slightly inclined loading causes measurable resistance. Our analysis paves the way towards a finite element model of silk fibers in which crystalline units can slide, move and rearrange themselves in the fiber during loading. PMID:25119288

  14. Viscous Friction between Crystalline and Amorphous Phase of Dragline Silk

    PubMed Central

    Patil, Sandeep P.; Xiao, Senbo; Gkagkas, Konstantinos; Markert, Bernd; Gräter, Frauke

    2014-01-01

    The hierarchical structure of spider dragline silk is composed of two major constituents, the amorphous phase and crystalline units, and its mechanical response has been attributed to these prime constituents. Silk mechanics, however, might also be influenced by the resistance against sliding of these two phases relative to each other under load. We here used atomistic molecular dynamics (MD) simulations to obtain friction forces for the relative sliding of the amorphous phase and crystalline units of Araneus diadematus spider silk. We computed the coefficient of viscosity of this interface to be in the order of 102 Ns/m2 by extrapolating our simulation data to the viscous limit. Interestingly, this value is two orders of magnitude smaller than the coefficient of viscosity within the amorphous phase. This suggests that sliding along a planar and homogeneous surface of straight polyalanine chains is much less hindered than within entangled disordered chains. Finally, in a simple finite element model, which is based on parameters determined from MD simulations including the newly deduced coefficient of viscosity, we assessed the frictional behavior between these two components for the experimental range of relative pulling velocities. We found that a perfectly relative horizontal motion has no significant resistance against sliding, however, slightly inclined loading causes measurable resistance. Our analysis paves the way towards a finite element model of silk fibers in which crystalline units can slide, move and rearrange themselves in the fiber during loading. PMID:25119288

  15. Biphasic surface amorphous layer lubrication of articular cartilage.

    PubMed

    Graindorge, Simon; Ferrandez, Wendy; Jin, Zhongmin; Ingham, Eileen; Grant, Colin; Twigg, Peter; Fisher, John

    2005-12-01

    The biphasic nature of articular cartilage has been acknowledged for some time and is known to play an important role in many of the biomechanical functions performed by this unique tissue. From the lubrication point of view however, a simple biphasic model is unable to account for the extremely low friction coefficients that have been recorded experimentally, particularly during start-up. In addition, research over the last decade has indicated the presence of a surface amorphous layer on top of articular cartilage. Here, we present results from a finite element model of articular cartilage that includes a thin, soft, biphasic surface amorphous layer (BSAL). The results of this study show that a thin BSAL, with lower elastic modulus, dramatically altered the load sharing between the solid and liquid phases of articular cartilage, particularly in the near-surface regions of the underlying bulk cartilage and within the surface amorphous layer itself where the fluid load support exceeded 85%. By transferring the load from the solid phase to the fluid phase, the biphasic surface layer improves lubrication and reduces friction, whilst also protecting the underlying cartilage surface by 'shielding' the solid phase from elevated stresses. The increase in lubrication effectiveness is shown to be greatest during short duration loading scenarios, such as shock loads.

  16. Atomic structure of intracellular amorphous calcium phosphate deposits.

    PubMed

    Betts, F; Blumenthal, N C; Posner, A S; Becker, G L; Lehninger, A L

    1975-06-01

    The radial distribution function calculated from x-ray diffraction of mineralized cytoplasmic structures isolated from the hepatopancreas of the blue crab (Callinectes sapidus) is very similar to that previously found for synthetic amorphous calcium phosphate. Both types of mineral apparently have only short-range atomic order, represented as a neutral ion cluster of about 10 A in longest dimension, whose probable composition is expressed by the formula Ca9(PO4)6. The minor differences observed are attributed to the presence in the biological mineral of significant amounts of Mg-2+ and ATP. Synthetic amorphous calcium phosphate in contact with a solution containing an amount of ATP equivalent to that of the biological mineral failed to undergo conversion to the thermodynamically more stable hydroxyapatite. The amorphous calcium phosphate of the cytoplasmic mineral granules is similarly stable, and does not undergo conversion to hydroxyapatite, presumably owing to the presence of ATP and Mg-2+, known in inhibitors of the conversion process. The physiological implications of mineral deposits consisting of stabilized calcium phosphate ion clusters are discussed.

  17. Amorphous stabilization and dissolution enhancement of amorphous ternary solid dispersions: combination of polymers showing drug-polymer interaction for synergistic effects.

    PubMed

    Prasad, Dev; Chauhan, Harsh; Atef, Eman

    2014-11-01

    The purpose of this study was to understand the combined effect of two polymers showing drug-polymer interactions on amorphous stabilization and dissolution enhancement of indomethacin (IND) in amorphous ternary solid dispersions. The mechanism responsible for the enhanced stability and dissolution of IND in amorphous ternary systems was studied by exploring the miscibility and intermolecular interactions between IND and polymers through thermal and spectroscopic analysis. Eudragit E100 and PVP K90 at low concentrations (2.5%-40%, w/w) were used to prepare amorphous binary and ternary solid dispersions by solvent evaporation. Stability results showed that amorphous ternary solid dispersions have better stability compared with amorphous binary solid dispersions. The dissolution of IND from the ternary dispersion was substantially higher than the binary dispersions as well as amorphous drug. Melting point depression of physical mixtures reveals that the drug was miscible in both the polymers; however, greater miscibility was observed in ternary physical mixtures. The IR analysis confirmed intermolecular interactions between IND and individual polymers. These interactions were found to be intact in ternary systems. These results suggest that the combination of two polymers showing drug-polymer interaction offers synergistic enhancement in amorphous stability and dissolution in ternary solid dispersions.

  18. Pressure-Induced Amorphization and a New High Density Amorphous Metallic Phase in Matrix-Free Ge Nanoparticles.

    PubMed

    Corsini, Niccolo R C; Zhang, Yuanpeng; Little, William R; Karatutlu, Ali; Ersoy, Osman; Haynes, Peter D; Molteni, Carla; Hine, Nicholas D M; Hernandez, Ignacio; Gonzalez, Jesus; Rodriguez, Fernando; Brazhkin, Vadim V; Sapelkin, Andrei

    2015-11-11

    Over the last two decades, it has been demonstrated that size effects have significant consequences for the atomic arrangements and phase behavior of matter under extreme pressure. Furthermore, it has been shown that an understanding of how size affects critical pressure-temperature conditions provides vital guidance in the search for materials with novel properties. Here, we report on the remarkable behavior of small (under ~5 nm) matrix-free Ge nanoparticles under hydrostatic compression that is drastically different from both larger nanoparticles and bulk Ge. We discover that the application of pressure drives surface-induced amorphization leading to Ge-Ge bond overcompression and eventually to a polyamorphic semiconductor-to-metal transformation. A combination of spectroscopic techniques together with ab initio simulations were employed to reveal the details of the transformation mechanism into a new high density phase-amorphous metallic Ge.

  19. Crystallization of amorphous indomethacin during dissolution: effect of processing and annealing.

    PubMed

    Greco, Kristyn; Bogner, Robin

    2010-10-01

    The crystallization of amorphous drugs during dissolution is a type of solution mediated phase transformation that can reduce the bioavailability enhancement one hoped to gain from the amorphous state. The goal of this study was to explore the effects of processing on the dissolution performance of amorphous indomethacin. The amorphous solids were prepared by four techniques, quench cooling the melted solid, cryogrinding γ indomethacin amorphous for 1 or 3 h and quench cooling the solid followed by 1 h of cryogrinding. Dissolution results assessed in a flow-through intrinsic dissolution apparatus reveal decreases in the dissolution rate of amorphous indomethacin during the experimental time frame indicating that a solution mediated phase transformation has occurred. The amorphous solids prepared by melt quenching and melt quenching followed by cryogrinding showed a significant dissolution rate advantage over the γ form of indomethacin. In contrast, indomethacin that was cryoground amorphous for 1 or 3 h did not show any dissolution rate advantage over the crystalline material. Transformation was confirmed by in situ Raman microscopy and polarized light microscopy with differences seen in the nature of the crystals apparent on the surface of the dissolving solid. A portion of the melt quenched amorphous sample was annealed at 25 °C and 0% relative humidity to induce partial crystallization of γ indomethacin. As crystallinity increased, the dissolution rate decreased. The transformation time of partially amorphous indomethacin was not dependent on the level of crystallinity present, indicating only a small fraction of crystalline material needs to be present to affect the kinetics of crystallization. The solution mediated phase transformation of amorphous indomethacin is affected by the processing method even though all solids were confirmed amorphous by polarized light microscopy and X-ray diffraction. Dissolution may distinguish differences in amorphous solids

  20. The impact of surface- and nano-crystallisation on the detected amorphous content and the dissolution behaviour of amorphous indomethacin.

    PubMed

    Priemel, P A; Grohganz, H; Gordon, K C; Rades, T; Strachan, C J

    2012-09-01

    The crystallinity and physical stability of amorphous drugs has previously been studied using different analytical techniques. However, the effect of the measurement method on observed crystallinity and its importance for critical quality attributes, such as dissolution, has not yet been widely investigated. The aim of this study was to (i) qualitatively analyse and understand the recrystallisation behaviour of amorphous indomethacin during storage, (ii) quantify the amorphous content during storage with complementary analytical techniques and (iii) investigate the relationship between observed recrystallisation behaviour and dissolution behaviour. Quench cooled indomethacin was stored and the samples were visualised by scanning electron microscopy to gain spatially resolved information about the recrystallisation behaviour. Crystallisation was quantified by Fourier transform attenuated total reflectance infrared (FT-ATR-IR) spectroscopy, differential scanning calorimetry and X-ray powder diffraction. These techniques resulted in different observed recrystallisation profiles. The physicochemical phenomena detected and sampling geometry for each technique together with the sample recrystallising from the surface and appearance of nano-crystals were used to explain the differences. The dissolution behaviour at the observed recrystallisation endpoints for the different analytical techniques revealed that FT-ATR-IR spectroscopy predicted the changes in dissolution behaviour due to crystallisation best.

  1. A Comparison of Photo-Induced Hysteresis Between Hydrogenated Amorphous Silicon and Amorphous IGZO Thin-Film Transistors.

    PubMed

    Ha, Tae-Jun; Cho, Won-Ju; Chung, Hong-Bay; Koo, Sang-Mo

    2015-09-01

    We investigate photo-induced instability in thin-film transistors (TFTs) consisting of amorphous indium-gallium-zinc-oxide (a-IGZO) as active semiconducting layers by comparing with hydrogenated amorphous silicon (a-Si:H). An a-IGZO TFT exhibits a large hysteresis window in the illuminated measuring condition but no hysteresis window in the dark condition. On the contrary, a large hysteresis window measured in the dark condition in a-Si:H was not observed in the illuminated condition. Even though such materials possess the structure of amorphous phase, optical responses or photo instability in TFTs looks different from each other. Photo-induced hysteresis results from initially trapped charges at the interface between semiconductor and dielectric films or in the gate dielectric which possess absorption energy to interact with deep trap-states and affect the movement of Fermi energy level. In order to support our claim, we also perform CV characteristics in photo-induced hysteresis and demonstrate thermal-activated hysteresis. We believe that this work can provide important information to understand different material systems for optical engineering which includes charge transport and band transition. PMID:26716230

  2. A Comparison of Photo-Induced Hysteresis Between Hydrogenated Amorphous Silicon and Amorphous IGZO Thin-Film Transistors.

    PubMed

    Ha, Tae-Jun; Cho, Won-Ju; Chung, Hong-Bay; Koo, Sang-Mo

    2015-09-01

    We investigate photo-induced instability in thin-film transistors (TFTs) consisting of amorphous indium-gallium-zinc-oxide (a-IGZO) as active semiconducting layers by comparing with hydrogenated amorphous silicon (a-Si:H). An a-IGZO TFT exhibits a large hysteresis window in the illuminated measuring condition but no hysteresis window in the dark condition. On the contrary, a large hysteresis window measured in the dark condition in a-Si:H was not observed in the illuminated condition. Even though such materials possess the structure of amorphous phase, optical responses or photo instability in TFTs looks different from each other. Photo-induced hysteresis results from initially trapped charges at the interface between semiconductor and dielectric films or in the gate dielectric which possess absorption energy to interact with deep trap-states and affect the movement of Fermi energy level. In order to support our claim, we also perform CV characteristics in photo-induced hysteresis and demonstrate thermal-activated hysteresis. We believe that this work can provide important information to understand different material systems for optical engineering which includes charge transport and band transition.

  3. [Microcosmic mechanisms of amorphous indomethacin crystallization and the influence of nano-coating on crystallization].

    PubMed

    Hui, Ou-Yang; Yi, Tao; Zheng, Qin; Liu, Feng

    2011-06-01

    Amorphous drugs have higher solubility, better oral bioavailability and are easier to be absorbed than their crystalline counterparts. However, the amorphous drugs, with weak stability, are so easy to crystallize that they will lose the original advantages. Polarization microscope, scanning electron microscope, differential scanning calorimetry, X-ray diffractomer and Raman spectroscopy were used to study the microcosmic crystallization mechanisms of amorphous indometacin and the performance of the drug crystals. The results showed that the growth rate of amorphous indometacin crystals at the free surface was markedly faster than that through the bulk, and that the crystal growth rate decreased observably after spraying an ultrathin melting gold (10 nm) at the free surface of the drug. These results indicated that the high growth rates of amorphous drugs crystals at the free surface were the key to their stability and that an ultrathin coating could be applied to enhance the stability of amorphous drugs.

  4. Using First-Principles Calculations to Describe Amorphous Metal Films for Hydrogen Purification

    NASA Astrophysics Data System (ADS)

    Hao, Shiqiang; Widom, Mike; Sholl, David

    2009-03-01

    The increasing demand for clean and efficient energy has resulted in an increased global willingness to embrace the proposed hydrogen economy. The use of amorphous metal films as membranes to purify hydrogen has potential to overcome at least some of the disadvantages of existing crystalline metal membranes. We introduce a general strategy combining density functional theory and statistical mechanics to quantitatively predict solubility, diffusivity and permeability of interstitial H in amorphous metals. Our methods make it possible for the first time to quantitatively evaluate the performance of amorphous metal films as hydrogen purification membranes. These methods are introduced by examining amorphous Fe3B and a crystalline analogue with the same composition. A membrane made from the amorphous material is predicted to have a hydrogen permeability 1.5-2 orders of magnitude higher than a crystalline membrane. The methods we introduce here will be useful in accelerating the development of amorphous membranes for practical applications.

  5. The structure of amorphous phases of ices prepared by high pressure and rapid quenching of water

    NASA Astrophysics Data System (ADS)

    Klug, Dennis D.; Tse, John S.; Tulk, Chris A.; Swainson, Ian; Svensson, Eric C.; Loong, C.-K.

    2000-03-01

    The structures of the amorphous ices are investigated using incoherent inelastic neutron scattering(1), neutron and x-ray scattering data, and reverse Monte Carlo methods to determine the relationship between liquid water under pressure or at 1 bar and the amorphous solids prepared by pressure amorphization and annealing or by rapid quenching of water. We show that the amorphous solids prepared by pressure amorphization are structurally different from liquid water and their structures are determined by the the mechanism for amorphization(2). References: 1) D.D. Klug, C.A. Tulk, E.C. Svensson, and C.-K. Loong, Phys. Rev. Lett. 83, 2584, 1999. 2) J.S. Tse, et al. Nature 400, 647 (1999).

  6. Evaluation of Si pre-amorphization for obtaining ultra-shallow junctions

    SciTech Connect

    Sultan, A.; Banerjee, S.; List, S.

    1996-12-31

    Two pre-amorphization techniques, shallow and deep amorphization using Si implants have been evaluated for obtaining shallow p-type junctions using B or BF2 implants followed by a Rapid Thermal Anneal (RTA) step. The effect on diffusion behavior and evolution of end-of-range dislocation loops has been studied experimentally using secondary ion mass spectrometry and planar and cross-sectional transmission electron microscopy. The shallow pre-amorphization followed by the dopant implant does not help in reduction of junction depth for either B or BF{sub 2} implants. Deep amorphization does help reduce junction depth. The pMOSFET leakage for deep amorphization scheme under a drain bias of 2.5 V is low ({approximately}pA/{mu}m). However, the reverse diode leakage for different diode structures for deep pre-amorphization is high ({approximately}nA) for a reverse bias of 3.6 V.

  7. HRTEM study of Popigai impact diamond: heterogeneous diamond nanostructures in native amorphous carbon matrix

    NASA Astrophysics Data System (ADS)

    Kis, Viktoria K.; Shumilova, Tatyana; Masaitis, Victor

    2016-10-01

    High-resolution transmission electron microscopy was applied for the detailed nanostructural investigation of Popigai impact diamonds with the aim of revealing the nature of the amorphous carbon of the matrix. The successful application of two complementary specimen preparation methods, focused ion beam (FIB) milling and mechanical cleavage, allowed direct imaging of nanotwinned nanodiamond crystals embedded in a native amorphous carbon matrix for the first time. Based on its stability under the electron beam, native amorphous carbon can be easily distinguished from the amorphous carbon layer produced by FIB milling during specimen preparation. Electron energy loss spectroscopy of the native amorphous carbon revealed the dominance of sp 2-bonded carbon and the presence of a small amount of oxygen. The heterogeneous size distribution and twin density of the nanodiamond crystals and the structural properties of the native amorphous carbon are presumably related to non-graphitic (organic) carbon precursor material.

  8. Reaction of amorphous Ni-W and Ni-N-W films with substrate silicon

    NASA Technical Reports Server (NTRS)

    Zhu, M. F.; Suni, I.; Nicolet, M.-A.; Sands, T.

    1984-01-01

    Wiley et al. (1982) have studied sputtered amorphous films of Nb-Ni, Mo-Ni, Si-W, and Si-Mo. Kung et al. (1984) have found that amorphous Ni-Mo films as diffusion barriers between multilayer metallizations on silicon demonstrate good electrical and thermal stability. In the present investigation, the Ni-W system was selected because it is similar to the Ni-Mo system. However, W has a higher silicide formation temperature than Mo. Attention is given to aspects of sample preparation, sample characterization, the interaction between amorphous Ni-W films and Si, the crystallization of amorphous Ni(36)W(64) films on SiO2, amorphous Ni-N-W films, silicide formation and phase separation, and the crystallization of amorphous Ni(36)W(64) and Ni(30)N(21)W(49) layers.

  9. Deformation-induced localized solid-state amorphization in nanocrystalline nickel

    PubMed Central

    Han, Shuang; Zhao, Lei; Jiang, Qing; Lian, Jianshe

    2012-01-01

    Although amorphous structures have been widely obtained in various multi-component metallic alloys, amorphization in pure metals has seldom been observed and remains a long-standing scientific curiosity and technological interest. Here we present experimental evidence of localized solid-state amorphization in bulk nanocrystalline nickel introduced by quasi-static compression at room temperature. High-resolution electron microscope observations illustrate that nano-scale amorphous structures present at the regions where severe deformation occurred, e.g. along crack paths or surrounding nano-voids. These findings have indicated that nanocrystalline structures are highly desirable for promoting solid-state amorphization, which may provide new insights for understanding the nature of the crystalline-to-amorphous transformation and suggested a potential method to produce elemental metallic glasses that have hardly been available hitherto through rapid solidification. PMID:22768383

  10. Recent advances in the characterization of amorphous pharmaceuticals by X-ray diffractometry.

    PubMed

    Thakral, Seema; Terban, Maxwell W; Thakral, Naveen K; Suryanarayanan, Raj

    2016-05-01

    For poorly water soluble drugs, the amorphous state provides an avenue to enhance oral bioavailability. The preparation method, in addition to sample history, can dictate the nature and the stability of the amorphous phase. Conventionally, X-ray powder diffractometry is of limited utility for characterization, but structural insights into amorphous and nanocrystalline materials have been enabled by coupling X-ray total scattering with the pair distribution function. This has shown great promise for fingerprinting, quantification, and even modeling of amorphous pharmaceutical systems. A consequence of the physical instability of amorphous phases is their crystallization propensity, and recent instrumental advances have substantially enhanced our ability to detect and quantify crystallization in a variety of complex matrices. The International Centre for Diffraction Data has a collection of the X-ray diffraction patterns of amorphous drugs and excipients and, based on the available supporting information, provides a quality mark of the data. PMID:26712710

  11. HRTEM study of Popigai impact diamond: heterogeneous diamond nanostructures in native amorphous carbon matrix

    NASA Astrophysics Data System (ADS)

    Kis, Viktoria K.; Shumilova, Tatyana; Masaitis, Victor

    2016-07-01

    High-resolution transmission electron microscopy was applied for the detailed nanostructural investigation of Popigai impact diamonds with the aim of revealing the nature of the amorphous carbon of the matrix. The successful application of two complementary specimen preparation methods, focused ion beam (FIB) milling and mechanical cleavage, allowed direct imaging of nanotwinned nanodiamond crystals embedded in a native amorphous carbon matrix for the first time. Based on its stability under the electron beam, native amorphous carbon can be easily distinguished from the amorphous carbon layer produced by FIB milling during specimen preparation. Electron energy loss spectroscopy of the native amorphous carbon revealed the dominance of sp 2-bonded carbon and the presence of a small amount of oxygen. The heterogeneous size distribution and twin density of the nanodiamond crystals and the structural properties of the native amorphous carbon are presumably related to non-graphitic (organic) carbon precursor material.

  12. Amorphous silica nanoparticles impair vascular homeostasis and induce systemic inflammation

    PubMed Central

    Nemmar, Abderrahim; Albarwani, Sulayma; Beegam, Sumaya; Yuvaraju, Priya; Yasin, Javed; Attoub, Samir; Ali, Badreldin H

    2014-01-01

    Amorphous silica nanoparticles (SiNPs) are being used in biomedical, pharmaceutical, and many other industrial applications entailing human exposure. However, their potential vascular and systemic pathophysiologic effects are not fully understood. Here, we investigated the acute (24 hours) systemic toxicity of intraperitoneally administered 50 nm and 500 nm SiNPs in mice (0.5 mg/kg). Both sizes of SiNPs induced a platelet proaggregatory effect in pial venules and increased plasma concentration of plasminogen activator inhibitor-1. Elevated plasma levels of von Willebrand factor and fibrinogen and a decrease in the number of circulating platelets were only seen following the administration of 50 nm SiNPs. The direct addition of SiNPs to untreated mouse blood significantly induced in vitro platelet aggregation in a dose-dependent fashion, and these effects were more pronounced with 50 nm SiNPs. Both sizes of SiNPs increased lactate dehydrogenase activity and interleukin 1β concentration. However, tumor necrosis factor α concentration was only increased after the administration of 50 nm SiNPs. Nevertheless, plasma markers of oxidative stress, including 8-isoprostane, thiobarbituric acid reactive substances, catalase, and glutathione S-transferase, were not affected by SiNPs. The in vitro exposure of human umbilical vein endothelial cells to SiNPs showed a reduced cellular viability, and more potency was seen with 50 nm SiNPs. Both sizes of SiNPs caused a decrease in endothelium-dependent relaxation of isolated small mesenteric arteries. We conclude that amorphous SiNPs cause systemic inflammation and coagulation events, and alter vascular reactivity. Overall, the effects observed with 50 nm SiNPs were more pronounced than those with 500 nm SiNPs. These findings provide new insight into the deleterious effect of amorphous SiNPs on vascular homeostasis. PMID:24936130

  13. Structural properties and energetics of amorphous forms of carbon

    NASA Astrophysics Data System (ADS)

    Kelires, P. C.

    1993-01-01

    We have made a comparative theoretical study of the most common forms of unhydrogenated amorphous carbon (α-C), namely, of the dense, diamondlike phase and the low-density evaporated α-C (e-C). Emphasis is given to the connection among the structure, energetics, and stability of these phases. To make the simulations of the amorphous structures (formed by quenching the liquid) tractable, we used the Monte Carlo method, combined with the empirical-potential approach. Our analysis employs a powerful total-energy-partitioning scheme, which is proved very useful in treating the energetics of disordered systems. It is found that threefold sp2 sites are the energetically favorable geometries in e-C, and thus they are by far more numerous. The nonplanar character of sp2 sites and the absence of sixfold rings indicate that medium-range order is rather not significant in e-C. The increasing graphitic character of e-C, as the temperature is raised, is explained by resorting to the effective temperatures T*, at which the atoms freeze in their lattice positions. For diamondlike α-C, the simulations show that there exist two distinctly different dense structures. The ``as-quenched'' one (i-C) is mostly sp3 bonded, but it is metastable. Upon annealing, it converts into a second phase (i-C*), mostly sp2 bonded, with a significant energy gain. A specific mechanism is proposed for this transition. The insensitivity of density to annealing is explained if we use the concept of the ``glass transition temperature'' T*. Finally, by introducing an isotropic bulk modulus for the amorphous phase, it is found that e-C has a much lower compressibility than i-C*, enhancing the distinguishability among the two low-coordinated forms of α-C.

  14. Mimas: Preliminary Evidence For Amorphous Water Ice From VIMS (Invited)

    NASA Astrophysics Data System (ADS)

    Cruikshank, D. P.; Marzo, G.; Pinilla-Alonso, N.; Roush, T. L.; Mastrapa, R. M.; Dalle Ore, C. M.; Buratti, B. J.; Stephan, K.; Brown, R. H.; Baines, K. H.; Clark, R. N.; Nicholson, P. D.; Sotin, C.; Cassini Vims Team

    2010-12-01

    We have conducted a statistical clustering analysis (1,2) on a mosaic of VIMS data cubes obtained on February 13, 2010, for Saturn’s satellite Mimas. Seven VIMS cubes were geometrically projected and re-sampled to a common spatial resolution. The clustering technique consists of a partitioning algorithm coupled to a criterion that prevents sub-optimal solutions and tests for the influence of random noise in the measurements. The clustering technique is agnostic about the meaning of the clusters, and scientific interpretation requires their a posteriori evaluation. The preliminary results yielded five clusters, demonstrating that spectral variability across Mimas’ surface is statistically significant. The ratios of the means calculated for each of the clusters show structure within the 1.6-µm water ice band, as well as the shape and the central wavelength of the strong ice band at 2 µm, that map spatially in patterns apparently related to the topography of Mimas, in particular certain regions in and around Herschel crater. The mean spectra of the five clusters, show similarities (band shape and central wavelength) with lab spectra of amorphous and crystalline H2O ice (3) that are suggestive of the presence of an amorphous (or “disordered”) ice component in certain regions of Mimas, notably on the central peak of Herschel, on the crater floor, and in faults surrounding the crater. Mimas is too warm to sustain H2O ice in a possibly original amorphous form for the great age of the surface, and its appearance may represent a mixture of both ice phases, or perhaps a layer of disordered ice on a base of crystalline ice. Another possible occurrence of non-crystalline ice appears southwest of Herschel, close to the south pole. (1) Marzo, G. A. et al. J. Geophys. Res. 111, E03002, 2006. (2) Marzo, G. A. et al. J. Geophys. Res. 113, E12009, 2008. (3) Mastrapa, R. M., et al. Astrophys. J. 701, 1347-1356, 2009.

  15. The glass transition in high-density amorphous ice

    PubMed Central

    Loerting, Thomas; Fuentes-Landete, Violeta; Handle, Philip H.; Seidl, Markus; Amann-Winkel, Katrin; Gainaru, Catalin; Böhmer, Roland

    2015-01-01

    There has been a long controversy regarding the glass transition in low-density amorphous ice (LDA). The central question is whether or not it transforms to an ultraviscous liquid state above 136 K at ambient pressure prior to crystallization. Currently, the most widespread interpretation of the experimental findings is in terms of a transformation to a superstrong liquid above 136 K. In the last decade some work has also been devoted to the study of the glass transition in high-density amorphous ice (HDA) which is in the focus of the present review. At ambient pressure HDA is metastable against both ice I and LDA, whereas at > 0.2 GPa HDA is no longer metastable against LDA, but merely against high-pressure forms of crystalline ice. The first experimental observation interpreted as the glass transition of HDA was made using in situ methods by Mishima, who reported a glass transition temperature Tg of 160 K at 0.40 GPa. Soon thereafter Andersson and Inaba reported a much lower glass transition temperature of 122 K at 1.0 GPa. Based on the pressure dependence of HDA's Tg measured in Innsbruck, we suggest that they were in fact probing the distinct glass transition of very high-density amorphous ice (VHDA). Very recently the glass transition in HDA was also observed at ambient pressure at 116 K. That is, LDA and HDA show two distinct glass transitions, clearly separated by about 20 K at ambient pressure. In summary, this suggests that three glass transition lines can be defined in the p–T plane for LDA, HDA, and VHDA. PMID:25641986

  16. Flexible amorphous silicon PIN diode x-ray detectors

    NASA Astrophysics Data System (ADS)

    Marrs, Michael; Bawolek, Edward; Smith, Joseph T.; Raupp, Gregory B.; Morton, David

    2013-05-01

    A low temperature amorphous silicon (a-Si) thin film transistor (TFT) and amorphous silicon PIN photodiode technology for flexible passive pixel detector arrays has been developed using active matrix display technology. The flexible detector arrays can be conformed to non-planar surfaces with the potential to detect x-rays or other radiation with an appropriate conversion layer. The thin, lightweight, and robust backplanes may enable the use of highly portable x-ray detectors for use in the battlefield or in remote locations. We have fabricated detector arrays up to 200 millimeters along the diagonal on a Gen II (370 mm x 470 mm rectangular substrate) using plasma enhanced chemical vapor deposition (PECVD) a-Si as the active layer and PECVD silicon nitride (SiN) as the gate dielectric and passivation. The a-Si based TFTs exhibited an effective saturation mobility of 0.7 cm2/V-s, which is adequate for most sensing applications. The PIN diode material was fabricated using a low stress amorphous silicon (a-Si) PECVD process. The PIN diode dark current was 1.7 pA/mm2, the diode ideality factor was 1.36, and the diode fill factor was 0.73. We report on the critical steps in the evolution of the backplane process from qualification of the low temperature (180°C) TFT and PIN diode process on the 150 mm pilot line, the transfer of the process to flexible plastic substrates, and finally a discussion and demonstration of the scale-up to the Gen II (370 x 470 mm) panel scale pilot line.

  17. Electron-beam-induced information storage in hydrogenated amorphous silicon devices

    DOEpatents

    Yacobi, B.G.

    1985-03-18

    A method for recording and storing information in a hydrogenated amorphous silicon device, comprising: depositing hydrogenated amorphous silicon on a substrate to form a charge collection device; and generating defects in the hydrogenated amorphous silicon device, wherein the defects act as recombination centers that reduce the lifetime of carriers, thereby reducing charge collection efficiency and thus in the charge collection mode of scanning probe instruments, regions of the hydrogenated amorphous silicon device that contain the defects appear darker in comparison to regions of the device that do not contain the defects, leading to a contrast formation for pattern recognition and information storage.

  18. Amorphous silicon carbide passivating layers for crystalline-silicon-based heterojunction solar cells

    SciTech Connect

    Boccard, Mathieu; Holman, Zachary C.

    2015-08-14

    Amorphous silicon enables the fabrication of very high-efficiency crystalline-silicon-based solar cells due to its combination of excellent passivation of the crystalline silicon surface and permeability to electrical charges. Yet, amongst other limitations, the passivation it provides degrades upon high-temperature processes, limiting possible post-deposition fabrication possibilities (e.g., forcing the use of low-temperature silver pastes). We investigate the potential use of intrinsic amorphous silicon carbide passivating layers to sidestep this issue. The passivation obtained using device-relevant stacks of intrinsic amorphous silicon carbide with various carbon contents and doped amorphous silicon are evaluated, and their stability upon annealing assessed, amorphous silicon carbide being shown to surpass amorphous silicon for temperatures above 300 °C. We demonstrate open-circuit voltage values over 700 mV for complete cells, and an improved temperature stability for the open-circuit voltage. Transport of electrons and holes across the hetero-interface is studied with complete cells having amorphous silicon carbide either on the hole-extracting side or on the electron-extracting side, and a better transport of holes than of electrons is shown. Also, due to slightly improved transparency, complete solar cells using an amorphous silicon carbide passivation layer on the hole-collecting side are demonstrated to show slightly better performances even prior to annealing than obtained with a standard amorphous silicon layer.

  19. Graphene growth by a metal-catalyzed solid-state transformation of amorphous carbon.

    PubMed

    Rodríguez-Manzo, Julio A; Pham-Huu, Cuong; Banhart, Florian

    2011-02-22

    Single and few-layer graphene is grown by a solid-state transformation of amorphous carbon on a catalytically active metal. The process is carried out and monitored in situ in an electron microscope. It is observed that an amorphous carbon film is taken up by Fe, Co, or Ni crystals at temperatures above 600 °C. The nucleation and growth of graphene layers on the metal surfaces happen after the amorphous carbon film has been dissolved. It is shown that the transformation of the energetically less favorable amorphous carbon to the more favorable phase of graphene occurs by diffusion of carbon atoms through the catalytically active metal.

  20. The structure and dynamics of amorphous and crystalline phases of ice

    SciTech Connect

    Klug, D. D.; Tse, J. S.; Tulk, C. A.; Svensson, E. C.; Swainson, I.; Loong, C.-K.

    2000-07-14

    The structures of the high and low-density amorphous phases of ice are studied using several techniques. The diffraction patterns of high and low density amorphous ice are analyzed using reverse Monte Carlo methods and compared with molecular dynamics simulations of these phases. The spectra of crystalline and amorphous phases of ice obtained by Raman and incoherent inelastic neutron scattering are analyzed to yield structural features for comparison with the results of molecular dynamics and Reverse Monte Carlo analysis. The structural details obtained indicate that there are significant differences between the structure of liquid water and the amorphous phases of ice.