Science.gov

Sample records for crystal field effects

  1. Crystal-field effects in fluoride crystals for optical refrigeration

    SciTech Connect

    Hehlen, Markus P

    2010-01-01

    thermal energy from the solid and carries it away as high-entropy light, thereby cooling the material. In the ideal case, the respective laser-cooling power is given by the pump wavelength ({lambda}{sub p}), the mean fluorescence wavelength ({bar {lambda}}{sub L}), and the absorption coefficient (a{sub r}) of the pumped transition. These quantities are solely determined by crystal field interactions. On one hand, a large crystal-field splitting offers a favorably large difference of {lambda}{sub p} - {bar {lambda}}{sub L} and thus a high cooling efficiency {eta}{sub cool} = ({lambda}{sub p} - {bar {lambda}}{sub L})/{bar {lambda}}{sub L}. On the other hand, a small crystal-field splitting offers a high thermal population (n{sub i}) of the initial state of the pumped transition, giving a high pump absorption coefficient and thus high laser cooling power, particularly at low temperatures. A quantitative description of crystal-field interactions is therefore critical to the understanding and optimization of optical refrigeration. In the case of Yb3+ as the laser cooling ion, however, development of a crystal-field model is met with substantial difficulties. First, Yb3+ has only two 4/multiplets, {sup 2}F{sub 7/2} and {sup 2}F{sub 5/2}, which lead to at most 7 crystal-field levels. This makes it difficult, and in some cases impossible, to evaluate the crystal-field Hamiltonian, which has at least 4 parameters for any Yb3+ point symmety lower than cubic. Second, {sup 2}F{sub 7/2}{leftrightarrow}{sup 2}F{sub 5/2} transitions exhibit an exceptionally strong electron-phonon coupling compared to 4f transitions of other rare earths. This makes it difficult to distinguish electronic from vibronic transitions in the absorption and luminescence spectra and to reliably identify the crystal-field levels. Yb3+ crystal-field splittings reported in the literature should thus generally be viewed with caution. This paper explores the effects of crystal-field interactions on the laser cooling

  2. Oxidation and crystal field effects in uranium

    NASA Astrophysics Data System (ADS)

    Tobin, J. G.; Yu, S.-W.; Booth, C. H.; Tyliszczak, T.; Shuh, D. K.; van der Laan, G.; Sokaras, D.; Nordlund, D.; Weng, T.-C.; Bagus, P. S.

    2015-07-01

    An extensive investigation of oxidation in uranium has been pursued. This includes the utilization of soft x-ray absorption spectroscopy, hard x-ray absorption near-edge structure, resonant (hard) x-ray emission spectroscopy, cluster calculations, and a branching ratio analysis founded on atomic theory. The samples utilized were uranium dioxide (U O2) , uranium trioxide (U O3) , and uranium tetrafluoride (U F4) . A discussion of the role of nonspherical perturbations, i.e., crystal or ligand field effects, will be presented.

  3. Oxidation and crystal field effects in uranium

    SciTech Connect

    Tobin, J. G.; Booth, C. H.; Shuh, D. K.; van der Laan, G.; Sokaras, D.; Weng, T. -C.; Yu, S. W.; Bagus, P. S.; Tyliszczak, T.; Nordlund, D.

    2015-07-06

    An extensive investigation of oxidation in uranium has been pursued. This includes the utilization of soft x-ray absorption spectroscopy, hard x-ray absorption near-edge structure, resonant (hard) x-ray emission spectroscopy, cluster calculations, and a branching ratio analysis founded on atomic theory. The samples utilized were uranium dioxide (UO2), uranium trioxide (UO3), and uranium tetrafluoride (UF4). As a result, a discussion of the role of non-spherical perturbations, i.e., crystal or ligand field effects, will be presented.

  4. Effects of magnetic fields on dissolution of arthritis causing crystals

    NASA Astrophysics Data System (ADS)

    Takeuchi, Y.; Iwasaka, M.

    2015-05-01

    The number of gout patients has rapidly increased because of excess alcohol and salt intake. The agent responsible for gout is the monosodium urate (MSU) crystal. MSU crystals are found in blood and consist of uric acid and sodium. As a substitute for drug dosing or excessive water intake, physical stimulation by magnetic fields represents a new medical treatment for gout. In this study, we investigated the effects of a magnetic field on the dissolution of a MSU crystal suspension. The white MSU crystal suspension was dissolved in an alkaline solution. We measured the light transmission of the MSU crystal suspension by a transmitted light measuring system. The magnetic field was generated by a horizontal electromagnet (maximum field strength was 500 mT). The MSU crystal suspension that dissolved during the application of a magnetic field of 500 mT clearly had a higher dissolution rate when compared with the control sample. We postulate that the alkali solution promoted penetration upon diamagnetic rotation and this magnetic field orienting is because of the pronounced diamagnetic susceptibility anisotropy of the MSU crystal. The results indicate that magnetic fields represent an effective gout treatment approach.

  5. Electromagnetic Field Effects in Semiconductor Crystal Growth

    NASA Technical Reports Server (NTRS)

    Dulikravich, George S.

    1996-01-01

    This proposed two-year research project was to involve development of an analytical model, a numerical algorithm for its integration, and a software for the analysis of a solidification process under the influence of electric and magnetic fields in microgravity. Due to the complexity of the analytical model that was developed and its boundary conditions, only a preliminary version of the numerical algorithm was developed while the development of the software package was not completed.

  6. Reflective liquid crystal light valve with hybrid field effect mode

    NASA Technical Reports Server (NTRS)

    Boswell, Donald D. (Inventor); Grinberg, Jan (Inventor); Jacobson, Alexander D. (Inventor); Myer, Gary D. (Inventor)

    1977-01-01

    There is disclosed a high performance reflective mode liquid crystal light valve suitable for general image processing and projection and particularly suited for application to real-time coherent optical data processing. A preferred example of the device uses a CdS photoconductor, a CdTe light absorbing layer, a dielectric mirror, and a liquid crystal layer sandwiched between indium-tin-oxide transparent electrodes deposited on optical quality glass flats. The non-coherent light image is directed onto the photoconductor; this reduces the impedance of the photoconductor, thereby switching the AC voltage that is impressed across the electrodes onto the liquid crystal to activate the device. The liquid crystal is operated in a hybrid field effect mode. It utilizes the twisted nematic effect to create a dark off-state (voltage off the liquid crystal) and the optical birefringence effect to create the bright on-state. The liquid crystal thus modulates the polarization of the coherent read-out or projection light responsively to the non-coherent image. An analyzer is used to create an intensity modulated output beam.

  7. TOPICAL REVIEW: Organic field-effect transistors using single crystals

    NASA Astrophysics Data System (ADS)

    Hasegawa, Tatsuo; Takeya, Jun

    2009-04-01

    Organic field-effect transistors using small-molecule organic single crystals are developed to investigate fundamental aspects of organic thin-film transistors that have been widely studied for possible future markets for 'plastic electronics'. In reviewing the physics and chemistry of single-crystal organic field-effect transistors (SC-OFETs), the nature of intrinsic charge dynamics is elucidated for the carriers induced at the single crystal surfaces of molecular semiconductors. Materials for SC-OFETs are first reviewed with descriptions of the fabrication methods and the field-effect characteristics. In particular, a benchmark carrier mobility of 20-40 cm2 Vs-1, achieved with thin platelets of rubrene single crystals, demonstrates the significance of the SC-OFETs and clarifies material limitations for organic devices. In the latter part of this review, we discuss the physics of microscopic charge transport by using SC-OFETs at metal/semiconductor contacts and along semiconductor/insulator interfaces. Most importantly, Hall effect and electron spin resonance (ESR) measurements reveal that interface charge transport in molecular semiconductors is properly described in terms of band transport and localization by charge traps.

  8. Crystal Field Handbook

    NASA Astrophysics Data System (ADS)

    Newman, D. J.; Ng, Betty

    2007-09-01

    List of contributors; Preface; Introduction; 1. Crystal field splitting mechanisms D. J. Newman and Betty Ng; 2. Empirical crystal fields D. J. Newman and Betty Ng; 3. Fitting crystal field parameters D. J. Newman and Betty Ng; 4. Lanthanide and actinide optical spectra G. K. Liu; 5. Superposition model D. J. Newman and Betty Ng; 6. Effects of electron correlation on crystal field splitting M. F. Reid and D. J. Newman; 7. Ground state splittings in S-state ions D. J. Newman and Betty Ng; 8. Invariants and moments Y. Y. Yeung; 9. Semiclassical model K. S. Chan; 10. Transition intensities M. F. Reid; Appendix 1. Point symmetry D. J. Newman and Betty Ng; Appendix 2. QBASIC programs D. J. Newman and Betty Ng; Appendix 3. Accessible program packages Y. Y. Yeung, M. F. Reid and D. J. Newman; Appendix 4. Computer package CST Cz. Rudowicz; Bibliography; Index.

  9. Effect of an electric field on nucleation and growth of crystals

    NASA Astrophysics Data System (ADS)

    Yurov, V. M.; Guchenko, S. A.; Gyngazova, M. S.

    2016-02-01

    The effect of the electric field strength on nucleation and growth of the crystals of ammonium halides and alkali metal sulfates has been studied. The optimal electric field strength for NH4Cl and NH4Br crystals was found to be 15 kV/cm, and for NH4I, it equaled 10 kV/cm. No effect of the electric field strength on the crystal growth was found for alkali metal sulfates. This difference is analyzed in terms of the crystal growth thermodynamics. In case, when the electric field is small and the Gibbs energy is of a significant value, the influence of the electric field at the crystal growth is negligible. A method to estimate the critical radius of homogeneous nucleation of the crystal is suggested.

  10. Spontaneous emission control of quantum dots embedded in photonic crystals: Effects of external fields and dimension

    NASA Astrophysics Data System (ADS)

    Vaseghi, B.; Hashemi, H.

    2016-06-01

    In this paper simultaneous effects of external electric and magnetic fields and quantum confinement on the radiation properties of spherical quantum dot embedded in a photonic crystal are investigated. Under the influence of photonic band-gap, effects of external static fields and dot dimension on the amplitude and spectrum of different radiation fields emitted by the quantum dot are studied. Our results show the considerable effects of external fields and quantum confinement on the spontaneous emission of the system.

  11. Electronic transitions, crystal field effects and phonons in UO 2

    NASA Astrophysics Data System (ADS)

    Schoenes, J.

    1980-08-01

    An extensive optical study of the 5f magnetic semiconductor UO 2 is presented. The experimental data include near normal incidence reflectivity measurements from 0.0025 to 13 eV, absorption and Faraday rotation measurements as function of temperature and of magnetic fields up to 100 kOe and photoemission results. From the data in the fundamental absorption region an energy level scheme is derived. This level scheme differs markedly from an earlier model but it is quantitatively supported by a calculation using the thermochemical Haber-Born process and also by cluster calculations. The localized nature of the 5f electrons is demonstrated. The absorption edge at 2 eV shows an abrupt shift to lower energies at the first order phase transition of UO 2 to the antiferromagnetic state. This shift is shown to be larger than expected from the lattice contraction indicating a magnetic order induced contribution to the total red shift. Below the absorption edge, intra-5f transitions and multiphonon excitations are reported, showing striking order induced effects at and below TN = 30.8 K. New results are presented for ε st, ε opt, ω TO and ω LO which fulfill the Lyddane-Sachs-Teller relation.

  12. Monitoring of hydroxyapatite crystal formation using field-effect transistor

    NASA Astrophysics Data System (ADS)

    Kajisa, Taira; Sakata, Toshiya

    2016-04-01

    The biomineralization process of hydroxyapatite (HAp) in simulated body fluid (SBF) was monitored in realtime using extended-gate FETs whose gate electrode was modified with a variety of alkanethiol self-assembled monolayers (SAMs). It was found that the gate surface potential of the carboxyl- and amino-group-terminated SAM-coated gate FET was increased in SBF as HAp crystals grew on the gate surface. Moreover, in the carboxyl-group-terminated SAM-coated gate FET, the rate of increase and the shift of gate surface potential of the FET were found to depend on the concentration of calcium ions in the SBF. It was concluded that the process of HAp crystallization at a SAM-modified surface can be detected using FETs. Thus, a FET device that enables the easy detection of ionic charges in a real-time and label-free manner, will be useful for evaluating biomaterials based on biomineralization such as those in the bone regeneration process.

  13. Determination of optimal ionic liquid for organic single-crystal field-effect transistors

    NASA Astrophysics Data System (ADS)

    Ono, S.; Miwa, K.; Seki, S.

    2016-02-01

    We investigate organic single-crystal field-effect transistors with various ionic liquids as gate dielectric. We find that the mobility of the field-effect transistors for both p-type and n-type organic semiconductors increases with decreasing total capacitance of the ionic liquid. However, it does not depend on the ion species at the interface between the organic semiconductor and the ionic liquid. By choosing an appropriate ionic liquid, a high carrier mobility of 12.4 cm2/V s in rubrene single crystals (p-type) and 0.13 cm2/V s in 7.7.8.8-Tetracyanoquinodimethane single crystals (n-type) are achieved. This study clarifies the influence of ionic liquids on the device performance of organic field-effect transistors and shows a way to maximize carrier mobility at the solid/liquid interface.

  14. Controlled deposition or organic semiconductor single crystals and its application in field-effect transistors

    NASA Astrophysics Data System (ADS)

    Liu, Shuhong

    The search for low-cost, large area, flexible devices has led to a remarkable increase in the research and development of organic semiconductors. Single-crystal organic field-effect transistors (OFETs) are ideal device structures for studying fundamental science associated with charge transport in organic materials and have demonstrated high mobility and outstanding electrical characteristics. For example, an exceptionally high carrier mobility of 20 cm2/Vs has been demonstrated for rubrene single crystal field effect transistors. However, it remains a technical challenge to integrate single-crystal devices into practical electronic applications. A key difficulty is that organic single-crystal devices are usually fabricated one device at a time by handpicking a single crystal and placing it onto the device substrate. This makes it impossible to mass-produce at high density with reasonable throughput. Therefore, there is a great need for a high-throughput method for depositing large arrays of organic semiconductor single crystals directly onto device structures. In this dissertation, I develop several approaches towards realizing this goal. The first approach is a solution-processing technique, which relies on solvent wetting and de-wetting on substrates with patterned wettability to selectively direct the deposition or removal of organic crystals. The assembly of different organic crystals over centimeter-squared areas on Au, SiO 2 and flexible plastic substrates is demonstrated. By designing line features on the substrate, alignment of needle-like crystals is also achieved. As a demonstration of the potential application of this approach, arrays of organic single crystal FETs are fabricated by patterning organic single crystals directly onto and between transistor source and drain electrodes. Besides organic single crystals, this self-assembly strategy is also applicable for patterning other objects such as metallic nanowires. In the second technique, organic

  15. Electric field effects on phase transitions in the 8CB liquid crystal doped with ferroelectric nanoparticles

    NASA Astrophysics Data System (ADS)

    Lin, Y.; Daoudi, A.; Segovia-Mera, A.; Dubois, F.; Legrand, C.; Douali, R.

    2016-06-01

    The influence of a low ac electric field on phase transitions is discussed in the case of a nematic liquid crystal 4 -n -octyl-4 '-cyanobiphenyl (8CB) doped with Sn2P2S6 ferroelectric nanoparticles. The phase-transition temperatures obtained from temperature-dependent dielectric measurements were higher than those determined by the calorimetric method. This difference is explained by the presence of the measuring electric field which induces two effects. The first one is the amplification of the interactions between the nanoparticle polarization and the liquid-crystal order parameter. The second one is the field-induced disaggregation or aggregation process at high nanoparticle concentrations.

  16. Diffraction and fringing field effects in small pixel liquid crystal devices with homeotropic alignment

    NASA Astrophysics Data System (ADS)

    Vanbrabant, Pieter J. M.; Beeckman, Jeroen; Neyts, Kristiaan; Willman, Eero; Fernandez, F. Anibal

    2010-10-01

    Reducing the pixel dimensions of liquid crystal microdisplays in search of high resolution has a fundamental impact on their electro-optic behavior. The liquid crystal director orientation becomes distorted due to fringing fields and diffraction effects influence the optical characteristics of the device once the structure features approach the wavelength of the incident light. Three-dimensional finite element simulation of the liquid crystal dynamics with a variable order approach is combined with a full-vector beam propagation analysis to investigate how elasticity and diffraction limit the resolution as a function of the pixel size for transmissive and reflective architectures with vertical liquid crystal alignment. The key liquid crystal properties are considered and the importance of materials with high birefringence is confirmed for small pixel devices as these improve the contrast for a fixed pixel size.

  17. Metal electrode dependent field effect transistors made of lanthanide ion-doped DNA crystals

    NASA Astrophysics Data System (ADS)

    Reddy Dugasani, Sreekantha; Hwang, Taehyun; Kim, Jang Ah; Gnapareddy, Bramaramba; Kim, Taesung; Park, Sung Ha

    2016-03-01

    We fabricated lanthanide ion (Ln3+, e.g. Dy3+, Er3+, Eu3+, and Gd3+)-doped self-assembled double-crossover (DX) DNA crystals grown on the surface of field effect transistors (FETs) containing either a Cr, Au, or Ni electrode. Here we demonstrate the metal electrode dependent FET characteristics as a function of various Ln3+. The drain-source current (I ds), controlled by the drain-source voltage (V ds) of Ln3+-doped DX DNA crystals with a Cr electrode on an FET, changed significantly under various gate voltages (V g) due to the relative closeness of the work function of Cr to the energy band gap of Ln3+-DNA crystals compared to those of Au and Ni. For Ln3+-DNA crystals on an FET with either a Cr or Ni electrode at a fixed V ds, I ds decreased with increasing V g ranging from  -2 to 0 V and from 0 to  +3 V in the positive and negative regions, respectively. By contrast, I ds for Ln3+-DNA crystals on an FET with Au decreased with increasing V g in only the positive region due to the greater electronegativity of Au. Furthermore, Ln3+-DNA crystals on an FET exhibited behaviour sensitive to V g due to the appreciable charge carriers generated from Ln3+. Finally, we address the resistivity and the mobility of Ln3+-DNA crystals on an FET with different metal electrodes obtained from I ds-V ds and I ds-V g curves. The resistivities of Ln3+-DNA crystals on FETs with Cr and Au electrodes were smaller than those of pristine DNA crystals on an FET, and the mobility of Ln3+-DNA crystals on an FET with Cr was relatively higher than that associated with other electrodes.

  18. Crystal field effect on EPR and optical absorption properties of natural green zoisite.

    PubMed

    Javier-Ccallata, Henry; Watanabe, Shigueo

    2013-03-01

    In this study the electron paramagnetic resonance (EPR) and optical absorption (OA) of natural crystal of zoisite were investigated after γ ((60)Co) irradiation and high temperature annealing. EPR measurements show that the zoisite from Tefilo Otoni MG Brazil contain Cr(3+), Fe(3+) and Mn(2+) ions and occupy distorted Al(3+) octahedral and tetrahedral sites which are subjected to the action of a strong crystal field in axial direction. Absorption bands which in principle give rise to sets of EPR lines between 500 and 2500 G were found using the deconvolution method. The application of high doses of gamma ray and high temperature annealing has shown no significant effects on EPR and OA spectra. Spin-allowed, spin-forbidden and crystal field parameters were calculated for 3d(3) configuration and interpreted using the spin Hamiltonian formalism containing axial and rhombic terms in low symmetries. PMID:23291113

  19. Electric field effects in nematic liquid crystals doped with carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Cîrtoaje, Cristina; Petrescu, Emil; Moţoc, Cornelia

    2013-12-01

    The aim of this paper was to investigate electric field induced effects in mixtures of nematic liquid crystals (NLCs) with positive electric anisotropies (MCL 6601 Merck) with carbon nanotubes (MWCNT from Aldrich). In planar alignment, the current-electric field dependence and the current-temperature dependence were explained by assuming a Poole-Frenkel effect (i.e. a tunnelling mechanism) and good agreement with the experimental data was obtained. Within this high field range it resulted that in planar aligned NLC-CNTs mixture the conductivity decreases when the temperature was increased. In homeotropic aligned mixture, the conduction mechanism is similar to the one occurring in a semiconductor: the conductivity increases when increasing temperature. This happens because in thin liquid crystal cells there is a possibility to realize an inner contact between nanotubes and electrodes so the mixture behaves like a semiconductor.

  20. Paramagnetic Meissner effect at high fields in YCaBaCuO single crystal

    NASA Astrophysics Data System (ADS)

    Dias, F. T.; Vieira, V. N.; Falck, A. L.; da Silva, D. L.; Pureur, P.; Schaf, J.

    2012-12-01

    We report on systematic magnetization experiments in an Y1-xCaxBa2Cu3O7-δ (x = 0.25 at%) single crystal. The magnetization experiments were made using a superconducting quantum interference device magnetometer (SQUID). Magnetic moments were measured as functions of the temperature according to the zero-field cooling (ZFC), field-cooled cooling (FCC), and field-cooled warming (FCW) prescriptions. The time-dependence of the FC magnetization at fixed magnetic fields was studied. Magnetic fields up to 50 kOe were applied and a paramagnetic response related to the superconducting state was observed when strong enough fields were applied parallel to the c axis. The magnitude of the high field paramagnetic moment (HFPME) increases when the field is augmented. The effect shows strong and anomalous time dependence, such that the paramagnetic moment increases as a function of the time. An YBa2Cu3O7-δ single crystal exhibiting the same effect was used for comparison. We discuss our results in terms of the flux compression scenario into the sample modulated by Ca concentration.

  1. Resistive memory effects in BiFeO3 single crystals controlled by transverse electric fields

    NASA Astrophysics Data System (ADS)

    Kawachi, S.; Kuroe, H.; Ito, T.; Miyake, A.; Tokunaga, M.

    2016-04-01

    The effects of electric fields perpendicular to the c-axis of the trigonal cell in single crystals of BiFeO3 are investigated through magnetization and resistance measurements. Magnetization and resistance exhibit hysteretic changes under applied electric fields, which can be ascribed to the reorientation of the magnetoelectric domains. Samples are repetitively switched between high- and low-resistance states by changing the polarity of the applied electric fields over 20 000 cycles at room temperature. These results demonstrate the potential of BiFeO3 for use in non-volatile memory devices.

  2. Effect of vertical magnetic field on convection and segregation in vertical Bridgman crystal growth

    NASA Technical Reports Server (NTRS)

    Kim, Do Hyun; Adornato, Peter M.; Brown, Robert A.

    1988-01-01

    A previous finite-element analysis of vertical Bridgman growth for dilute and nondilute alloys is extended to include the effect of a vertically-aligned magnetic field in the limit of zero magnetic Reynolds number. Calculations are presented for growth of a dilute gallium-germanium alloy in a vertically stabilized Bridgman-Stockbarger system and in a furnace with a uniform temperature gradient imposed along the ampoule. Steady cellular convection driven by radial temperature gradients causes good axial and radial mixing in both systems without a magnetic field. A weak magnetic field decreases the intensity of convection and the effectiveness of solute mixing. The radial nonuniformity is greatest for an intermediate field strength. Stronger fields suppress flow recirculation completely, and lead to uniform solute segregation across the crystal and to diffusion-controlled axial segregation.

  3. The Effects of a Magnetic Field on the Crystallization of a Fluorozirconate Glass

    NASA Technical Reports Server (NTRS)

    Tucker, Dennis S.; Lapointe, Michael R.; Jia, Zhiyong

    2006-01-01

    An axial magnetic field of 0.1T was applied to ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fibers during heating to the glass crystallization temperature. Scanning electron microscopy and x-ray diffraction were used to identify crystal phases. It was shown that fibers exposed to the magnetic field did not crystallize while fibers not exposed to the field did crystallize. A hypothesis based on magnetic work was proposed to explain the results and tested by measuring the magnetic susceptibilities of the glass and crystal.

  4. Light quasiparticles dominate electronic transport in molecular crystal field-effect transistors

    SciTech Connect

    Li, Z. Q.; Podzorov, V.; Sai, N.; Martin, Michael C.; Gershenson, M. E.; Di Ventra, M.; Basov, D. N.

    2007-03-01

    We report on an infrared spectroscopy study of mobile holes in the accumulation layer of organic field-effect transistors based on rubrene single crystals. Our data indicate that both transport and infrared properties of these transistors at room temperature are governed by light quasiparticles in molecular orbital bands with the effective masses m[small star, filled]comparable to free electron mass. Furthermore, the m[small star, filled]values inferred from our experiments are in agreement with those determined from band structure calculations. These findings reveal no evidence for prominent polaronic effects, which is at variance with the common beliefs of polaron formation in molecular solids.

  5. Effect of intense magnetic fields on the convection of biogenic guanine crystals in aqueous solution

    NASA Astrophysics Data System (ADS)

    Iwasaka, M.; Mizukawa, Y.

    2015-05-01

    In this study, the basic magneto-optic properties of biogenic microcrystals in aqueous media were investigated. Microcrystals, mica plates, silica, and microcrystals from a diatom cell and biogenic guanine crystals from goldfish showed light scattering inhibition when the crystals were observed in water under a 5 T magnetic field and dark-field illumination. In particular, in 50% ethanol/water medium, convection of the biogenic guanine particle aggregates was reversibly inhibited when the microcrystal suspension was exposed to a 5 T magnetic field. Microscopic observation comparing the biogenic guanine crystals in water with 95% ethanol or 99% acetone revealed that light flickering on the surface of the crystals was affected by the surface interaction of the crystal with the surrounding medium. By considering both the magnetic orientation of the microcrystals and the possible interactions of crystals with the surrounding medium, a magnetically controllable fluidic tracer was suggested.

  6. Transferred large area single crystal MoS2 field effect transistors

    NASA Astrophysics Data System (ADS)

    Lee, Choong Hee; McCulloch, William; Lee, Edwin W.; Ma, Lu; Krishnamoorthy, Sriram; Hwang, Jinwoo; Wu, Yiying; Rajan, Siddharth

    2015-11-01

    Transfer of epitaxial, two-dimensional (2D) MoS2 on sapphire grown via synthetic approaches is a prerequisite for practical device applications. We report centimeter-scale, single crystal, synthesized MoS2 field effect transistors (FETs) transferred onto SiO2/Si substrates, with a field-effect mobility of 4.5 cm2 V-1 s-1, which is among the highest mobility values reported for the transferred large-area MoS2 transistors. We demonstrate simple and clean transfer of large-area MoS2 films using deionized water, which can effectively avoid chemical contamination. The transfer method reported here allows standard i-line stepper lithography process to realize multiple devices over the entire film area.

  7. Oxygen content and crystal field effects in RBa sub 2 Cu sub 3 O sub x

    SciTech Connect

    Podlesnyak, A.A.; Mirmelstein, A.V.; Bobrovskii, V.I.; Zhadhin, I.L.; Blinovskov, Y.N.; Kozhenvnikov, V.L.; Goshchitskii, B.N. )

    1991-05-10

    Effects of crystal electrical field (CEF) in the orthorhombic phase of RBa{sub 2}Cu{sub 3}O{sub x} (R = Ho, Er; x = 6.9, 6.4) are investigated by inelastic magnetic neutron scattering (IMNS). The level schemes of the lowest multiplet of 4f-shell of the rare-earth ion are found. In this paper it is shown that the experimental scattering spectra and their variation depending on the oxygen content may be explained by spacial distribution of the negative charge within the unit cell.

  8. Rubrene crystal field-effect mobility modulation via conducting channel wrinkling

    PubMed Central

    Reyes-Martinez, Marcos A.; Crosby, Alfred J.; Briseno, Alejandro L.

    2015-01-01

    With the impending surge of flexible organic electronic technologies, it has become essential to understand how mechanical deformation affects the electrical performance of organic thin-film devices. Organic single crystals are ideal for the systematic study of strain effects on electrical properties without being concerned about grain boundaries and other defects. Here we investigate how the deformation affects the field-effect mobility of single crystals of the benchmark semiconductor rubrene. The wrinkling instability is used to apply local strains of different magnitudes along the conducting channel in field-effect transistors. We discover that the mobility changes as dictated by the net strain at the dielectric/semiconductor interface. We propose a model based on the plate bending theory to quantify the net strain in wrinkled transistors and predict the change in mobility. These contributions represent a significant step forward in structure–function relationships in organic semiconductors, critical for the development of the next generation of flexible electronic devices. PMID:25939864

  9. Rubrene crystal field-effect mobility modulation via conducting channel wrinkling.

    PubMed

    Reyes-Martinez, Marcos A; Crosby, Alfred J; Briseno, Alejandro L

    2015-01-01

    With the impending surge of flexible organic electronic technologies, it has become essential to understand how mechanical deformation affects the electrical performance of organic thin-film devices. Organic single crystals are ideal for the systematic study of strain effects on electrical properties without being concerned about grain boundaries and other defects. Here we investigate how the deformation affects the field-effect mobility of single crystals of the benchmark semiconductor rubrene. The wrinkling instability is used to apply local strains of different magnitudes along the conducting channel in field-effect transistors. We discover that the mobility changes as dictated by the net strain at the dielectric/semiconductor interface. We propose a model based on the plate bending theory to quantify the net strain in wrinkled transistors and predict the change in mobility. These contributions represent a significant step forward in structure-function relationships in organic semiconductors, critical for the development of the next generation of flexible electronic devices. PMID:25939864

  10. Effect of far-field flow on a columnar crystal in the convective undercooled melt

    NASA Astrophysics Data System (ADS)

    Ji, Xiao-Jian; Chen, Ming-Wen; Xu, Xiao-Hua; Wang, Zi-Dong

    2015-01-01

    The growth behavior of a columnar crystal in the convective undercooled melt affected by the far-field uniform flow is studied and the asymptotic solution for the interface evolution of the columnar crystal is derived by means of the asymptotic expansion method. The results obtained reveal that the far-field flow induces a significant change of the temperature around the columnar crystal and the convective flow caused by the far-field flow accelerates the growth velocity of the interface of the growing columnar crystal in the upstream direction and inhibits its growth velocity in the downstream direction. Our results are similar to the experimental data and numerical simulations. Project supported by the Overseas Distinguished Scholar Program by the Ministry of Education of China (Grant No. MS2010BJKJ005), the National Natural Science Foundation of China (Grant No. 10972030), and the Science and Technology Support Project of Jiangxi, China (Grant No. 20112BBE50006).

  11. Ferroelectric Single-Crystal Gated Graphene/Hexagonal-BN/Ferroelectric Field-Effect Transistor.

    PubMed

    Park, Nahee; Kang, Haeyong; Park, Jeongmin; Lee, Yourack; Yun, Yoojoo; Lee, Jeong-Ho; Lee, Sang-Goo; Lee, Young Hee; Suh, Dongseok

    2015-11-24

    The effect of a ferroelectric polarization field on the charge transport in a two-dimensional (2D) material was examined using a graphene monolayer on a hexagonal boron nitride (hBN) field-effect transistor (FET) fabricated using a ferroelectric single-crystal substrate, (1-x)[Pb(Mg1/3Nb2/3)O3]-x[PbTiO3] (PMN-PT). In this configuration, the intrinsic properties of graphene were preserved with the use of an hBN flake, and the influence of the polarization field from PMN-PT could be distinguished. During a wide-range gate-voltage (VG) sweep, a sharp inversion of the spontaneous polarization affected the graphene channel conductance asymmetrically as well as an antihysteretic behavior. Additionally, a transition from antihysteresis to normal ferroelectric hysteresis occurred, depending on the V(G) sweep range relative to the ferroelectric coercive field. We developed a model to interpret the complex coupling among antihysteresis, current saturation, and sudden conductance variation in relation with the ferroelectric switching and the polarization-assisted charge trapping, which can be generalized to explain the combination of 2D structured materials with ferroelectrics. PMID:26487348

  12. Crystal field and magnetic properties

    NASA Technical Reports Server (NTRS)

    Flood, D. J.

    1977-01-01

    Magnetization and magnetic susceptibility measurements have been made in the temperature range 1.3 to 4.2 K on powdered samples of ErH3. The susceptibility exhibits Curie-Weiss behavior from 4.2 to 2 K, and intercepts the negative temperature axis at theta = 1.05 + or - 0.05 K, indicating that the material is antiferromagnetic. The low field effective moment is 6.77 + or - 0.27 Bohr magnetons per ion. The magnetization exhibits a temperature independent contribution, the slope of which is (5 + or - 1.2) x 10 to the -6th Weber m/kg Tesla. The saturation moment is 3.84 + or - 1 - 0.15 Bohr magnetons per ion. The results can be qualitatively explained by the effects of crystal fields on the magnetic ions. No definitive assignment of a crystal field ground state can be given, nor can a clear choice between cubically or hexagonally symmetric crystal fields be made. For hexagonal symmetry, the first excited state is estimated to be 86 to 100 K above the ground state. For cubic symmetry, the splitting is on the order of 160 to 180 K.

  13. Phase-field study of crystal growth in three-dimensional capillaries: Effects of crystalline anisotropy.

    PubMed

    Debierre, Jean-Marc; Guérin, Rahma; Kassner, Klaus

    2016-07-01

    Phase-field simulations are performed to explore the thermal solidification of a pure melt in three-dimensional capillaries. Motivated by our previous work for isotropic or slightly anisotropic materials, we focus here on the more general case of anisotropic materials. Different channel cross sections are compared (square, hexagonal, circular) to reveal the influence of geometry and the effects of a competition between the crystal and the channel symmetries. In particular, a compass effect toward growth directions favored by the surface energy is identified. At given undercooling and anisotropy, the simulations generally show the coexistence of several growth modes. The relative stability of these growth modes is tested by submitting them to a strong spatiotemporal noise for a short time, which reveals a subtle hierarchy between them. Similarities and differences with experimental growth modes in confined geometry are discussed qualitatively. PMID:27575207

  14. Phase-field study of crystal growth in three-dimensional capillaries: Effects of crystalline anisotropy

    NASA Astrophysics Data System (ADS)

    Debierre, Jean-Marc; Guérin, Rahma; Kassner, Klaus

    2016-07-01

    Phase-field simulations are performed to explore the thermal solidification of a pure melt in three-dimensional capillaries. Motivated by our previous work for isotropic or slightly anisotropic materials, we focus here on the more general case of anisotropic materials. Different channel cross sections are compared (square, hexagonal, circular) to reveal the influence of geometry and the effects of a competition between the crystal and the channel symmetries. In particular, a compass effect toward growth directions favored by the surface energy is identified. At given undercooling and anisotropy, the simulations generally show the coexistence of several growth modes. The relative stability of these growth modes is tested by submitting them to a strong spatiotemporal noise for a short time, which reveals a subtle hierarchy between them. Similarities and differences with experimental growth modes in confined geometry are discussed qualitatively.

  15. Effects of the biaxial transverse crystal-field on the phase diagrams of a spin-1 nanowire

    NASA Astrophysics Data System (ADS)

    Magoussi, H.; Zaim, A.; Boughrara, M.; Kerouad, M.

    2016-09-01

    By using the effective field theory based on a probability distribution method, the phase diagrams and the magnetic properties of an Ising nanowire in the presence of the biaxial transverse crystal-field are investigated. The effects of the biaxial transverse crystal field, the interfacial coupling and the exchange interaction in the surface on the phase diagram, the magnetization and the internal energy are examined. Some characteristic phenomena are found such as the tricritical behavior, the critical end point and the re-entrant phenomenon.

  16. Field Control of the Surface Electroclinic Effect in Liquid Crystal Displays II

    NASA Astrophysics Data System (ADS)

    Zappitelli, Kara; Hipolite, Dana; Saunders, Karl

    2012-11-01

    As previously introduced in the presentation by Dana Hipolite, chiral, smectic liquid crystal molecules aligned in layers can be controlled by the application of an electric field, which has a variety of implications for the quality of LCD displays. Both the bulk electroclinic effect (BECE) and surface electroclinic effect (SECE) impact the angle at which the molecules tilt with respect to the director in different areas of the cell. Certain LC's exhibit a continuous Sm-A* to Sm-C* transition, where the angle of the surface and bulk molecules change continually with the electric field. Other LC's exhibit first order transitions where we see jumps in the tilt at different values of the applied electric field for the bulk and surface molecules respectively. The difference in angle of the bulk and surface molecules in both of these situations causes discrepancies in the layer spacing within the LC cell. These discrepancies lead to frustrations within the cell, which can be quantified by the strain (?). These frustrations can be relieved in multiple ways, however the method of relief may lead to negative impacts on the alignment quality of the display itself.

  17. Enhanced mobility in organic field-effect transistors due to semiconductor/dielectric interface control and very thin single crystal

    NASA Astrophysics Data System (ADS)

    Dong, Ji; Yu, Peng; Atika Arabi, Syeda; Wang, Jiawei; He, Jun; Jiang, Chao

    2016-07-01

    A perfect organic crystal while keeping high quality semiconductor/dielectric interface with minimal defects and disorder is crucial for the realization of high performance organic single crystal field-effect transistors (OSCFETs). However, in most reported OSCFET devices, the crystal transfer processes is extensively used. Therefore, the semiconductor/dielectric interface is inevitably damaged. Carrier traps and scattering centers are brought into the conduction channel, so that the intrinsic high mobility of OSCFET devices is entirely disguised. Here, very thin pentacene single crystal is grown directly on bare SiO2 by developing a ‘seed-controlled’ pentacene single crystal method. The interface quality is controlled by an in situ fabrication of OSCFETs. The interface is kept intact without any transfer process. Furthermore, we quantitatively analyze the influence of crystal thickness on device performance. With a pristine interface and very thin crystal, we have achieved the highest mobility: 5.7 cm2 V‑1 s‑1—more than twice the highest ever reported pentacene OSCFET mobility on bare SiO2. This study may provide a universal route for the use of small organic molecules to achieve high performance in lamellar single crystal field-effect devices.

  18. Effect of temperature and electric field on 2D nematic colloidal crystals stabilised by vortex-like topological defects.

    PubMed

    Zuhail, K P; Dhara, Surajit

    2016-08-10

    We report experimental studies on 2D colloidal crystals of dimers stabilized by vortex-like defects in planar nematic and π/2 twisted nematic cells. The dimers are prepared and self-assembled using a laser tweezer. We study the effect of temperature and electric field on the lattice parameters of the colloidal crystals. The lattice parameters vary with the temperature in the nematic phase and a discontinuous structural change is observed at the nematic to smectic-A phase transition. In the nematic phase, we observed a large change in the lattice parameters (≃30%) by applying an external electric field perpendicular to the plane of the 2D crystals. The idea and the active control of the lattice parameters could be useful for designing tunable colloidal crystals. PMID:27445255

  19. Solitary waves in two-dimensional dusty plasma crystal: Effects of weak magnetic field

    SciTech Connect

    Ghosh, Samiran; Gupta, M. R.

    2010-03-15

    It is shown that in the presence of weak magnetic field, the dust lattice solitary wave in two-dimensional (2D) hexagonal dusty plasma crystal is governed by a gyration-modified 2D Korteweg-de Vries equation due to the action of Lorentz force on the dust particles. Numerical solutions reveal that only for weak magnetic field an apparently single hump solitary wave solution exist. But, for strong magnetic field dust lattice solitary wave becomes unstable showing repetitive solitary hump of increasing magnitude with time.

  20. Crystal-Field and Covalency Effects in Uranates: An X-ray Spectroscopic Study.

    PubMed

    Butorin, Sergei M; Kvashnina, Kristina O; Smith, Anna L; Popa, Karin; Martin, Philippe M

    2016-07-01

    The electronic structure of U(V) - and U(VI) -containing uranates NaUO3 and Pb3 UO6 was studied by using an advanced technique, namely X-ray absorption spectroscopy (XAS) in high-energy-resolution fluorescence-detection (HERFD) mode. Due to a significant reduction in core-hole lifetime broadening, the crystal-field splittings of the 5f shell were probed directly in HERFD-XAS spectra collected at the U 3d edge, which is not possible by using conventional XAS. In addition, the charge-transfer satellites that result from U 5f-O 2p hybridization were clearly resolved. The crystal-field parameters, 5f occupancy, and degree of covalency of the chemical bonding in these uranates were estimated by using the Anderson impurity model by calculating the U 3d HERFD-XAS, conventional XAS, core-to-core (U 4f-3d transitions) resonant inelastic X-ray scattering (RIXS), and U 4f X-ray photoelectron spectra. The crystal field was found to be strong in these systems and the 5f occupancy was determined to be 1.32 and 0.84 electrons in the ground state for NaUO3 and Pb3 UO6 , respectively, which indicates a significant covalent character for these compounds. PMID:27257782

  1. Effect of an electric field on the magnetization of a SmFe3(BO3)4 single crystal

    NASA Astrophysics Data System (ADS)

    Freidman, A. L.; Balaev, A. D.; Dubrovskii, A. A.; Eremin, E. V.; Shaikhutdinov, K. A.; Temerov, V. L.; Gudim, I. A.

    2015-07-01

    A change in the magnetization of a SmFe3(BO3)4 single crystal in response to an applied alternating electric field has been experimentally observed for the first time. The measurements have demonstrated that the magnetization oscillates not only at a frequency of the applied electric field but also at twice the frequency. The dependences of the magnetoelectric effect on the magnetic and electric fields and temperature have been measured. It has been assumed that the existence of the second harmonic of the magnetoelectric effect is due to the electrostriction.

  2. Magnetic anisotropy and crystalline electric field effects in RRh{sub 4}B{sub 4} single crystals.

    SciTech Connect

    Zhou, H.; Lambert, S. E.; Maple, M. B.; Dunlap, B. D.; Materials Science Division; Univ. of California at San Diego

    2009-08-01

    Research on polycrystalline RRh{sub 4}B{sub 4} samples has shown that crystalline electric field (CEF) effects play an important role in these compounds. The successful synthesis of single crystal samples of RRh{sub 4}B{sub 4} with R = Y, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu has provided an opportunity to further investigate CEF effects in these materials. Magnetization and magnetic susceptibility measurements on the RRh{sub 4}B{sub 4} single crystals revealed strong magnetic anisotropy, and the experimental results could be described well by CEF calculations based on the parameters derived from an analysis of experimental data for ErRh{sub 4}B{sub 4} single crystals. The easy directions of magnetization of these compounds are consistent with the signs of the Stevens factor {alpha}J of the CEF Hamiltonian. A strong influence of magnetic anisotropy on superconductivity was also observed.

  3. Touch sensors based on planar liquid crystal-gated-organic field-effect transistors

    SciTech Connect

    Seo, Jooyeok; Lee, Chulyeon; Han, Hyemi; Lee, Sooyong; Nam, Sungho; Kim, Youngkyoo; Kim, Hwajeong; Lee, Joon-Hyung; Park, Soo-Young; Kang, Inn-Kyu

    2014-09-15

    We report a tactile touch sensor based on a planar liquid crystal-gated-organic field-effect transistor (LC-g-OFET) structure. The LC-g-OFET touch sensors were fabricated by forming the 10 μm thick LC layer (4-cyano-4{sup ′}-pentylbiphenyl - 5CB) on top of the 50 nm thick channel layer (poly(3-hexylthiophene) - P3HT) that is coated on the in-plane aligned drain/source/gate electrodes (indium-tin oxide - ITO). As an external physical stimulation to examine the tactile touch performance, a weak nitrogen flow (83.3 μl/s) was employed to stimulate the LC layer of the touch device. The LC-g-OFET device exhibited p-type transistor characteristics with a hole mobility of 1.5 cm{sup 2}/Vs, but no sensing current by the nitrogen flow touch was measured at sufficiently high drain (V{sub D}) and gate (V{sub G}) voltages. However, a clear sensing current signal was detected at lower voltages, which was quite sensitive to the combination of V{sub D} and V{sub G}. The best voltage combination was V{sub D} = −0.2 V and V{sub G} = −1 V for the highest ratio of signal currents to base currents (i.e., signal-to-noise ratio). The change in the LC alignment upon the nitrogen flow touch was assigned as the mechanism for the present LC-g-OFET touch sensors.

  4. Dependence of Pentacene Crystal Growth on Dielectric Roughness for Fabrication of Flexible Field-Effect Transistors

    SciTech Connect

    Yang, H.; Yang, C; Kim, S; Jang, M; Park, C

    2010-01-01

    The dependence of pentacene nanostructures on gate dielectric surfaces were investigated for flexible organic field-effect transistor (OFET) applications. Two bilayer types of polymer/aluminum oxide (Al{sub 2}O{sub 3}) gate dielectrics were fabricated on commercial Al foils laminated onto a polymer back plate. Some Al foils were directly used as gate electrodes, and others were smoothly polished by an electrolytic etching. These Al surfaces were then anodized and coated with poly({alpha}-methyl styrene) (PAMS). For PAMS/Al{sub 2}O{sub 3} dielectrics onto etched Al foils, surface roughness up to 1 nm could be reached, although isolated dimples with a lateral diameter of several micrometers were still present. On PAMS/Al{sub 2}O{sub 3} dielectrics (surface roughness >40 nm) containing mechanical grooves of Al foil, average hole mobility ({mu}FET) of 50 nm thick pentacene-FETs under the low operating voltages (|V| < 6 V) was {approx}0.15 cm{sup 2} V{sup -1} s{sup -1}. In contrast, pentacene-FETs employing the etched Al gates exhibited {mu}FET of 0.39 cm{sup 2} V{sup -1} s{sup -1}, which was comparable to that of reference samples with PAMS/Al{sub 2}O{sub 3} dielectrics onto flat sputtered Al gates. Conducting-probe atomic force microscopy and two-dimensional X-ray diffraction of pentacene films with various thicknesses revealed different out-of-plane and in-plane crystal orderings of pentacene, depending on the surface roughness of the gate dielectrics.

  5. Field-induced phase transitions in an antiferroelectric liquid crystal using the pyroelectric effect

    PubMed

    Shtykov; Vij; Lewis; Hird; Goodby

    2000-08-01

    The antiferroelectric liquid crystal (AFLC) under investigation possesses different helical polar phases. Measurements of pyroelectric response of these phases as a function of temperature and bias field have elucidated the ability of this method for investigating the nature of antiferroelectric phases and phase transitions under the bias field. The pyroelectric signal as a function of the bias field at fixed temperatures and as a function of temperature for fixed bias fields was measured for different phases of the investigated AFLC material. A theoretical model describing the pyroelectric response in different phases of AFLC is given, and the experimental results are interpreted. The threshold fields for field induced phase transitions are determined. The type of field induced phase transition from the AF phase in particular is found to be dependent on the temperature within its range. The properties of an unusual ferrielectric phase existing between ferrielectric chiral smectic-C (SmC*) and antiferroelectric AF phases are studied in a great detail. The results confirm that this phase is one of the incommensurate phases, predicted by the axial next-nearest neighbor Ising model and Landau model for this temperature region. PMID:11088695

  6. Effects of polarized organosilane self-assembled monolayers on organic single-crystal field-effect transistors

    NASA Astrophysics Data System (ADS)

    Takeya, J.; Nishikawa, T.; Takenobu, T.; Kobayashi, S.; Iwasa, Y.; Mitani, T.; Goldmann, C.; Krellner, C.; Batlogg, B.

    2004-11-01

    The surface conductivity is measured by a four-probe technique for pentacene and rubrene single crystals laminated on polarized and nearly unpolarized molecular monolayers with application of perpendicular electric fields. The polarization of the self-assembled monolayers (SAMs) shifts the threshold gate voltage, while maintaining a very low subthreshold swing of the single-crystal devices (0.11 V/decade). The results, excluding influences of parasitic contacts and grain boundaries, demonstrate SAM-induced nanoscale charge injection up to ˜1012cm-2 at the surface of the organic single crystals.

  7. Giant rotating magnetocaloric effect at low magnetic fields in multiferroic TbMn2O5 single crystals

    NASA Astrophysics Data System (ADS)

    Balli, M.; Jandl, S.; Fournier, P.; Dimitrov, D. Z.

    2016-03-01

    In conventional magnetocaloric refrigeration systems, the magnetocaloric effect is exploited by moving the active material in and out of the magnetic field source. Here, we demonstrate that a large and reversible magnetocaloric effect (-ΔSR, max = 6.4 J/kg K and ΔTR, max = 8 K under 2 T) can be generated simply by rotating the multiferroic TbMn2O5 single crystal around its b axis in a relatively low constant magnetic field applied in the ac plane. Our results should inspire and open ways toward the implementation of compact, efficient and embedded magnetocaloric devices for low temperature and space applications.

  8. Metastable Copper-Phthalocyanine Single-Crystal Nanowires and Their Use in Fabricating High-Performance Field-Effect Transistors

    SciTech Connect

    Xiao, Kai; Li, Rongjin; Tao, Jing; Payzant, E Andrew; Ivanov, Ilia N; Puretzky, Alexander A; Hu, Wenping; Geohegan, David B

    2009-01-01

    This paper describes a simple, vapor-phase route to the synthesis of metastable α-phase copper-phthalocyanine (CuPc) single-crystal nanowires through control of the growth temperature. The influence of the growth temperature on the crystal structures, morphology, and size of the CuPc nanostructures was explored by XRD, optical absorption and Transmission Electron Microscopy (TEM). α-CuPc nanowires were successfully incorporated as active semiconductors in field-effect transistors (FETs). Single nanowire devices exhibited the carrier mobilities and current on/off ratios as high as 0.4 cm2/Vs and > 104, respectively, rendering them useful for organic photovoltaic cells, organic light-emitting diodes, field-effect transistors, memories and gas sensors

  9. Effect of Magnetic Fields on g-jitter Induced Convection and Solute Striation During Space Processing of Single Crystals

    NASA Technical Reports Server (NTRS)

    deGroh, H. C.; Li, K.; Li, B. Q.

    2002-01-01

    A 2-D finite element model is presented for the melt growth of single crystals in a microgravity environment with a superimposed DC magnetic field. The model is developed based on the deforming finite element methodology and is capable of predicting the phenomena of the steady and transient convective flows, heat transfer, solute distribution, and solid-liquid interface morphology associated with the melt growth of single crystals in microgravity with and without an applied magnetic field. Numerical simulations were carried out for a wide range of parameters including idealized microgravity conditions, the synthesized g-jitter and the real g-jitter data taken by on-board accelerometers during space flights. The results reveal that the time varying g-jitter disturbances, although small in magnitude, cause an appreciable convective flow in the liquid pool, which in turn produces detrimental effects during the space processing of single crystal growth. An applied magnetic field of appropriate strength, superimposed on microgravity, can be very effective in suppressing the deleterious effects resulting from the g-jitter disturbances.

  10. Effect of crystal-field splitting and interband hybridization on the metal-insulator transitions of strongly correlated systems

    NASA Astrophysics Data System (ADS)

    Poteryaev, Alexander I.; Ferrero, Michel; Georges, Antoine; Parcollet, Olivier

    2008-07-01

    We investigate a quarter-filled two-band Hubbard model involving a crystal-field splitting, which lifts the orbital degeneracy as well as an interorbital hopping (interband hybridization). Both terms are relevant to the realistic description of correlated materials such as transition-metal oxides. The nature of the Mott metal-insulator transition is clarified and is found to depend on the magnitude of the crystal-field splitting. At large values of the splitting, a transition from a two-band to a one-band metal is first found as the on-site repulsion is increased and is followed by a Mott transition for the remaining band, which follows the single-band (Brinkman-Rice) scenario well documented previously within dynamical mean-field theory. At small values of the crystal-field splitting, a direct transition from a two-band metal to a Mott insulator with partial orbital polarization is found, which takes place simultaneously for both orbitals. This transition is characterized by a vanishing of the quasiparticle weight for the majority orbital but has a first-order character for the minority orbital. It is pointed out that finite-temperature effects may easily turn the metallic regime into a bad metal close to the orbital polarization transition in the metallic phase.

  11. Partial Dissolution of Charge Order Phase Observed in β-(BEDT-TTF)2PF6 Single Crystal Field Effect Transistor.

    PubMed

    Sakai, Masatoshi; Moritoshi, Norifumi; Kuniyoshi, Shigekazu; Yamauchi, Hiroshi; Kudo, Kazuhiro; Masu, Hyuma

    2016-04-01

    The effect of an applied gate electric field on the charge-order phase in β-(BEDT-TTF)2PF6 single-crystal field-effect transistor structure was observed at around room temperature by technical improvement with respect to sample preparation and electrical measurements. A relatively slight but systematic increase of the electrical conductance induced by the applied gate electric field and its temperature dependence was observed at around the metal-insulator transition temperature (TMI). The temperature dependence of the modulated electrical conductance demonstrated that TMI was shifted toward the lower side by application of a gate electric field, which corresponds to partial dissolution of the charge-order phase. The thickness of the partially dissolved charge order region was estimated to be several score times larger than the charge accumulation region. PMID:27451615

  12. Effects of composition and temperature on the large-field behavior of [001]C relaxor single crystals.

    PubMed

    Gallagher, John; Lynch, Christopher; Tian, Jian

    2014-12-01

    The compositional dependence of the large-field behavior of [001]C-cut relaxor ferroelectric xPb(In1/2Nb1/2) O3-(1-x-y)Pb(Mg1/3Nb2/3)O3-yPbTiO3 (PIN-PMN-PT) single crystals that are on the rhombohedral side of the morphotropic phase boundary was characterized under electrical, mechanical, and thermal loading. The effects of varying the concentrations of PIN and PT are discussed. Composition was found to impact the material constants and the field-induced phase transformation threshold in the piezoelectric d333-mode configuration. PMID:25474790

  13. Single-crystal field-effect transistors of new Cl2-NDI polymorph processed by sublimation in air

    NASA Astrophysics Data System (ADS)

    He, Tao; Stolte, Matthias; Burschka, Christian; Hansen, Nis Hauke; Musiol, Thomas; Kälblein, Daniel; Pflaum, Jens; Tao, Xutang; Brill, Jochen; Würthner, Frank

    2015-01-01

    Physical properties of active materials built up from small molecules are dictated by their molecular packing in the solid state. Here we demonstrate for the first time the growth of n-channel single-crystal field-effect transistors and organic thin-film transistors by sublimation of 2,6-dichloro-naphthalene diimide in air. Under these conditions, a new polymorph with two-dimensional brick-wall packing mode (β-phase) is obtained that is distinguished from the previously reported herringbone packing motif obtained from solution (α-phase). We are able to fabricate single-crystal field-effect transistors with electron mobilities in air of up to 8.6 cm2 V-1 s-1 (α-phase) and up to 3.5 cm2 V-1 s-1 (β-phase) on n-octadecyltriethoxysilane-modified substrates. On silicon dioxide, thin-film devices based on β-phase can be manufactured in air giving rise to electron mobilities of 0.37 cm2 V-1 s-1. The simple crystal and thin-film growth procedures by sublimation under ambient conditions avoid elaborate substrate modifications and costly vacuum equipment-based fabrication steps.

  14. Near infrared Kerr effect and description of field-induced phase transitions in polymer-stabilized blue phase liquid crystals

    NASA Astrophysics Data System (ADS)

    Atorf, B.; Rasouli, H.; Nordendorf, G.; Wilkes, D.; Kitzerow, H.

    2016-02-01

    Studies of the influence of an electric field E on the effective refractive index of a polymer-stabilized blue phase in the near infrared spectral range reveal a considerable field-induced birefringence. At moderate voltages, the birefringence increases linearly with the square of the field strength as expected for the electro-optic Kerr effect, with an effective Kerr constant of K ≈ 6.3 - 6.9 × 10-10 m V-2. However, for E > ≈7.3 V/μm, the slope of the field-induced birefringence versus E2 increases abruptly, before saturation is reached at E > ≈8.5 V/μm. Based on previous observations on blue phases in the visible wavelength range, the discontinuous change can be attributed to a field-induced phase transition. A modification of the extended Kerr model introduced by Wu and coworkers is suggested to take this additional effect into account. In addition to the promising properties of blue phases for improved liquid crystal displays, the observed field-induced birefringence in the infrared region opens interesting perspectives for telecommunication and other non-display applications.

  15. Fabrication of graphene field-effect transistor on top of ferroelectric single-crystal substrate

    NASA Astrophysics Data System (ADS)

    Park, Nahee; Kang, Haeyong; Lee, Yourack; Kim, Jeong-Gyun; Kim, Joong-Gyu; Yun, Yoojoo; Park, Jeongmin; Kim, Taesoo; Kim, Jung Ho; Jin, Youngjo; Shin, Yong Seon; Lee, Young Hee; Suh, Dongseok

    2015-03-01

    In the analysis of Graphene field-effect transistor, the substrate material which has the direct contact with Graphene layer plays an important in the device performance. In this presentation, we have tested PMN-PT(i.e.(1-x)Pb(Mg1/3Nb2/3) O3-xPbTiO3) substrate as a gate dielectric of Graphene field-effect transistor. Unlike the case of previously used substrates such as silicon oxide or hexagonal Boron-Nitride(h-BN), the PMN-PT substrate can induce giant amount of surface charge that is directly injected to the attached Graphene layer due to its ferroelectric property. And the hysteresis of polarization versus electric field of PMN-PT can cause the device to show the ferroelectric nonvolatile memory operation. We had successfully fabricated Graphene field-effect transistor using the mechanically exfoliated Graphene layer transferred on the PMN-PT(001) substrate. Unlike the case of mechanical exfoliation on the surface of silicon-oxide or the Poly(methyl methacrylate) (PMMA), the weak adhesion properties between graphene and PMNPT required the pretreatment on PMMA before the exfoliation process. The device performance is analyzed in terms of the effect of ferro- and piezo-electric effect of PMNPT substrate.

  16. Effect of Crystal Fields in Ho1 - xDyxNi2B2 C

    NASA Astrophysics Data System (ADS)

    Lee, W. C.

    2013-03-01

    From the anisotropy and the temperature dependence of magnetic susceptibilities of Ho1 - x Dyx Ni2B2 C system with magnetic field H perpendicular or parallel to c-axis, the crystalline electric field (CEF) effect has been studied and the magnetic exchange interaction constant Jex of rare-earth ions perpendicular to the c-axis estimated for 0 <=x <=1. The crystalline electric field parameter, B02, the first Steven parameter and the most dominant term in this system, are determined from the high-temperature-limit anisotropic Weiss temperatures of the magnetic susceptibilities and there is a broad minimum around x ~ 0.3, where superconducting transition temperature, TC, and Néel temperature, TN, are almost same.

  17. Anisotropy of the upper critical fields and the paramagnetic Meissner effect in La1.85Sr0.15CuO4 single crystals.

    PubMed

    Felner, I; Tsindlekht, M I; Drachuck, G; Keren, A

    2013-02-13

    Optimally doped La(1.85)Sr(0.15)CuO(4) single crystals have been investigated by dc and ac magnetic measurements. These crystals have rectangular needle-like shapes with the long needle axis parallel to the crystallographic c axis (c-crystal) or parallel to the basal planes (a-crystal). In both crystals, the temperature dependence of the upper critical fields (H(C2)) and the surface critical field (H(C3)) were measured. The H-T phase diagram is presented. Close to T(C) = 35 K, for the c-crystal, γ(C) = H(C3)(c)/H(C2)(c) = 1.80(2), whereas for the a-crystal the γ(a) = H(C3)(a)/H(C2)(a) = 4.0(2) obtained is much higher than 1.69, predicted by the ideal mathematical model. At low applied dc fields, positive field-cooled branches known as the 'paramagnetic Meissner effect' (PME) are observed; their magnitude is inversely proportional to H. The anisotropic PME is observed in both a- and c-crystals, only when the applied field is along the basal planes. It is speculated that the high γ(a) and the PME are connected to each other. PMID:23315336

  18. Effect of two-dimensional confinement on switching of vertically aligned liquid crystals by an in-plane electric field.

    PubMed

    Choi, Tae-Hoon; Woo, Jae-Hyeon; Choi, Yeongyu; Yoon, Tae-Hoon

    2016-09-01

    We investigated the two-dimensional (2-D) confinement effect of liquid crystals (LCs) on the switching of vertically aligned LCs by an in-plane electric field. When an in-plane field is applied to a vertical alignment (VA) cell, virtual walls are built at the center of the interdigitated electrodes and at the middle of the gaps between them. The LC molecules are confined not only by the two substrates but also by the virtual walls so that the turn-off time of a VA cell driven by an in-plane field is dependent on the pitch of the interdigitated electrodes as well as the cell gap. Therefore, the turn-off time of a VA cell driven by an in-plane field can be reduced simply by decreasing the pitch of the interdigitated electrodes as a result of the enhanced anchoring provided by the virtual walls. The experimental results showed good agreement with a simple model based on the 2-D confinement effect of LCs. PMID:27607702

  19. Electrostimulation of the magnetoplastic effect in LiF crystals by an "internal" electric field induced during indentation

    NASA Astrophysics Data System (ADS)

    Galustashvili, M. V.; Driaev, D. G.; Akopov, F. Kh.; Tsakadze, S. D.

    2013-08-01

    Indented LiF crystals demonstrate a change in the length of the dislocation rosette rays during their exposure to jointly acting dc magnetic and electric fields. It is shown that magnetic field with induction B = 1 T causes the electrostimulation or electrosuppression depending on the magnitude and direction of the external electric field with respect to the "internal" electric field induced by the charge transfer due to dislocations moving during the indentation.

  20. Unusual Kondo-hole effect and crystal-field frustration in Nd-doped CeRhIn5

    NASA Astrophysics Data System (ADS)

    Rosa, P. F. S.; Oostra, A.; Thompson, J. D.; Pagliuso, P. G.; Fisk, Z.

    2016-07-01

    We investigate single crystals of Ce1 -xNdxRhIn5 by means of x-ray-diffraction, microprobe, magnetic susceptibility, heat capacity, and electrical resistivity measurements. Our data reveal that the antiferromagnetic transition of CeRhIn5, at TNCe=3.8 K, is linearly suppressed with xNd. We associate this effect with the presence of a "Kondo hole" created by Nd substitution. The extrapolation of TNCe to zero temperature, however, occurs at xc˜0.3 , which is below the two-dimensional percolation limit found in Ce1 -xLaxRhIn5 . This result strongly suggests the presence of a crystal-field induced magnetic frustration. Near xNd˜0.2 , the Ising antiferromagnetic order from Nd3 + ions is stabilized and TNNd increases up to 11 K in NdRhIn5. Our results shed light on the effects of magnetic doping in heavy-fermion antiferromagnets and stimulate the study of such systems under applied pressure.

  1. Enhanced mobility in organic field-effect transistors due to semiconductor/dielectric iInterface control and very thin single crystal.

    PubMed

    Dong, Ji; Yu, Peng; Arabi, Syeda Atika; Wang, Jiawei; He, Jun; Jiang, Chao

    2016-07-01

    A perfect organic crystal while keeping high quality semiconductor/dielectric interface with minimal defects and disorder is crucial for the realization of high performance organic single crystal field-effect transistors (OSCFETs). However, in most reported OSCFET devices, the crystal transfer processes is extensively used. Therefore, the semiconductor/dielectric interface is inevitably damaged. Carrier traps and scattering centers are brought into the conduction channel, so that the intrinsic high mobility of OSCFET devices is entirely disguised. Here, very thin pentacene single crystal is grown directly on bare SiO2 by developing a 'seed-controlled' pentacene single crystal method. The interface quality is controlled by an in situ fabrication of OSCFETs. The interface is kept intact without any transfer process. Furthermore, we quantitatively analyze the influence of crystal thickness on device performance. With a pristine interface and very thin crystal, we have achieved the highest mobility: 5.7 cm(2) V(-1) s(-1)-more than twice the highest ever reported pentacene OSCFET mobility on bare SiO2. This study may provide a universal route for the use of small organic molecules to achieve high performance in lamellar single crystal field-effect devices. PMID:27211506

  2. Crystal growth of CdTe in space and thermal field effects on mass flux and morphology

    NASA Technical Reports Server (NTRS)

    Wiedemeier, H.

    1988-01-01

    The primary, long-range goals are the development of vapor phase crystal growth experiments, and the growth of technologically useful crystals in space. The necessary ground-based studies include measurements of the effects of temperature variations on the mass flux and crystal morphology in vapor-solid growth processes. For in-situ mass flux measurements dynamic microbalance techniques will be employed. Crystal growth procedures and equipment will be developed to be compatible with microgravity conditions and flight requirements. Emphasis was placed on the further development of crystal growth and the investigation of relevant transport properties of CdTe. The dependence of the mass flux on source temperature was experimentally established. The CdTe synthesis and pretreatment procedures are being developed that yield considerable improvements in mass transport rates, and mass fluxes which are independent of the amount of source material. A higher degree of stoichiometric control of CdTe than before was achieved during this period of investigation. Based on this, a CdTe crystal growth experiment, employing physical vapor transport, yielded very promising results. Optical microscopy and X-ray diffraction studies revealed that the boule contained several large sized crystal grains of a high degree of crystallinity. Further characterization studies of CdTe crystals are in progress. The reaction chamber, furnace dimensions, and ampoule location of the dynamic microbalance system were modified in order to minimize radiation effects on the balance performance.

  3. Effective long-range interlayer interactions and electric-field-induced subphases in ferrielectric liquid crystals

    NASA Astrophysics Data System (ADS)

    Chandani, A. D. L.; Fukuda, Atsuo; Vij, Jagdish K.; Takanishi, Yoichi; Iida, Atsuo

    2016-04-01

    Microbeam resonant x-ray scattering experiments recently revealed the sequential emergence of electric-field-induced subphases (stable states) with exceptionally large unit cells consisting of 12 and 15 smectic layers. We explain the emergence of the field-induced subphases by the quasimolecular model based on the Emelyanenko-Osipov long-range interlayer interactions (LRILIs) together with our primitive way of understanding the frustration in clinicity using the qE number defined as qE=|[R ] -[L ] | /([R ] +[L ] ) ; here [R ] and [L ] refer to the numbers of smectic layers with directors tilted to the right and to the left, respectively, in the unit cell of a field-induced subphase. We show that the model actually stabilizes the field-induced subphases with characteristic composite unit cells consisting of several blocks, each of which is originally a ferrielectric three-layer unit cell stabilized by the LRILIs, but some of which would be modified to become ferroelectric by an applied electric field. In a similar line of thought, we also try to understand the puzzling electric-field-induced birefringence data in terms of the LRILIs.

  4. Liquid crystal-gated-organic field-effect transistors with in-plane drain-source-gate electrode structure.

    PubMed

    Seo, Jooyeok; Nam, Sungho; Jeong, Jaehoon; Lee, Chulyeon; Kim, Hwajeong; Kim, Youngkyoo

    2015-01-14

    We report planar liquid crystal-gated-organic field-effect transistors (LC-g-OFETs) with a simple in-plane drain-source-gate electrode structure, which can be cost-effectively prepared by typical photolithography/etching processes. The LC-g-OFET devices were fabricated by forming the LC layer (4-cyano-4'-pentylbiphenyl, 5CB) on top of the channel layer (poly(3-hexylthiophene), P3HT) that was spin-coated on the patterned indium-tin oxide (ITO)-coated glass substrates. The LC-g-OFET devices showed p-type transistor characteristics, while a current saturation behavior in the output curves was achieved for the 50-150 nm-thick P3HT (channel) layers. A prospective on/off ratio (>1 × 10(3)) was obtained regardless of the P3HT thickness, whereas the resulting hole mobility (0.5-1.1 cm(2)/(V s)) at a linear regime was dependent on the P3HT thickness. The tilted ordering of 5CB at the LC-P3HT interfaces, which is induced by the gate electric field, has been proposed as a core point of working mechanism for the present LC-g-OFETs. PMID:25478816

  5. Effect of 10-T magnetic fields on structural colors in guanine crystals of fish scales

    NASA Astrophysics Data System (ADS)

    Iwasaka, M.; Miyashita, Y.; Kudo, M.; Kurita, S.; Owada, N.

    2012-04-01

    This work reports the magnetically modulated structural colors in the chromatophore of goldfish scales under static magnetic fields up to 10 T. A fiber optic system for spectroscopy measurements and a CCD microscope were set in the horizontal bore of a 10-T superconducting magnet. One leaf of a fish scale was set in a glass chamber, exposed to visible light from its side direction, and then static magnetic fields were applied perpendicular to the surface of the scale. In addition, an optical fiber for spectroscopy was directed perpendicular to the surface. During the magnetic field sweep-up, the aggregate of guanine thin plates partially showed a rapid light quenching under 0.26 to 2 T; however, most of the thin plates continued to scatter the side-light and showed changing iridescence, which was displayed individually by each guanine plate. For example, an aggregate in the chromatophore exhibited a dynamic change in structural color from white-green to dark blue when the magnetic fields changed from 2 to 10 T. The spectrum profile, which was obtained by the fiber optic system, confirmed the image color changes under magnetic field exposure. Also, a linearly polarized light transmission was measured on fish scales by utilizing an optical polarizer and analyzer. The transmitted polarized light intensities increased in the range of 500-550 nm compared to the intensity at 700 nm during the magnetic field sweep-up. These results indicate that the multi-lamella structure of nano-mirror plates in guanine hexagonal micro-plates exhibit diamagnetically modulated structure changes, and its light interference is affected by strong magnetic fields.

  6. Random crystal field effect on the kinetic spin-3/2 Blume-Capel model under a time-dependent oscillating field

    NASA Astrophysics Data System (ADS)

    El Hachimi, A. G.; Dakir, O.; Sidi Ahmed, S.; Zaari, H.; El Yadari, M.; Benyoussef, A.; El Kenz, A.

    2016-09-01

    The effect of random crystal-field on the stationary states of the kinetic spin-3/2 Blume-Capel model is investigated within the framework of the mean-field approach. The Glauber-type stochastic dynamics is used to describe the time evolution of the system which is subject to a time-dependent oscillating external magnetic field. In addition to the well-known phase transitions and the appearance of the partly ferromagnetic phase characterized by the magnetization m = 1 in equilibrium case, a new dynamical regions between the ferromagnetic phases F1/2, F1 and F3/2 are found where F3/2 +F 1 / 2 ,F3/2 +F1, F1 +F1/2 phases coexist for a weak value of the reduced magnetic field (h). Whereas for higher value of h both solutions ordered F and disordered P phases coexist. Hence we present six types topologies of phase diagrams which exhibit dynamical first-order, second-order transition lines, dynamical tricritical and isolated critical end points. Furthermore, the dynamical thermal behavior magnetizations, susceptibilities and phase space trajectories are given and discussed.

  7. Effects of three-dimensional polymer networks in vertical alignment liquid crystal display controlled by in-plane field.

    PubMed

    Lim, Young Jin; Choi, Young Eun; Lee, Jun Hee; Lee, Gi-Dong; Komitov, Lachezar; Lee, Seung Hee

    2014-05-01

    Polymer network in vertical alignment liquid crystal cell driven by in-plane field (VA-IPS) is formed in three dimensions to achieve fast response time and to keep the liquid crystal alignment even when an external pressure is applied to the cell. The network formed by UV irradiation to vertically aligned liquid crystal cell with reactive mesogen does not disturb a dark state while exhibiting very fast decaying response time less than 2ms in all grey scales and almost zero pooling mura. The proposed device has a strong potential to be applicable to field sequential display owing to super-fast response time and flexible display owing to polymer network in bulk which supports a gap between two substrates. PMID:24921764

  8. A new real-time non-coherent to coherent light image converter - The hybrid field effect liquid crystal light valve

    NASA Technical Reports Server (NTRS)

    Grinberg, J.; Jacobson, A.; Bleha, W.; Miller, L.; Fraas, L.; Boswell, D.; Myer, G.

    1975-01-01

    A new, high-performance device has been developed for application to real-time coherent optical data processing. The new device embodies a CdS photoconductor, a CdTe light-absorbing layer, a dielectric mirror, and a liquid crystal layer sandwiched between indium-tin-oxide transparent electrodes deposited on optical quality glass flats. The noncoherent image is directed onto the photoconductor; this reduces the impedance of the photoconductor, thereby switching the ac voltage that is impressed across the electrodes onto the liquid crystal to activate the device. The liquid crystal is operated in a hybrid field effect mode. It utilizes the twisted nematic effect to create a dark off-state and the optical birefringence effect to create the bright on-state. The liquid crystal modulates the polarization of the coherent read-out light so an analyzer must be used to create an intensity modulated output beam.

  9. Effect of an electric field on the orientation of a liquid crystal in a cell with a nonuniform director distribution

    NASA Astrophysics Data System (ADS)

    Aksenova, E. V.; Karetnikov, A. A.; Karetnikov, N. A.; Kovshik, A. P.; Ryumtsev, E. I.; Sakhatskii, A. S.; Svanidze, A. V.

    2016-05-01

    The electric field-induced reorientation of a nematic liquid crystal in cells with a planar helicoidal or a homeoplanar structure of a director field is studied theoretically and experimentally. The dependences of the capacitances of these systems on the voltage in an applied electric field below and above the Fréedericksz threshold are experimentally obtained and numerically calculated. The calculations use the director distribution in volume that is obtained by direct minimization of free energy at various voltages. The inhomogeneity of the electric field inside a cell is taken into account. The calculation results are shown to agree with the experimental data.

  10. Effect of electric field and temperature gradient on the orientational dynamics of liquid crystals in a microvolume cylindrical cavity

    NASA Astrophysics Data System (ADS)

    Zakharov, A. V.; Vakulenko, A. A.; Romano, Silvano

    2009-10-01

    We have considered a homogeneously aligned liquid crystal (HALC) microvolume confined between two infinitely long horizontal coaxial cylinders and investigated dynamic field pumping, i.e., studied the interactions between director, velocity, and electric E fields as well as a radially applied temperature gradient ∇T, where the inner cylinder is kept at a lower temperature than the outer one. In order to elucidate the role of ∇T in producing hydrodynamic flow u, we have carried out a numerical study of a system of hydrodynamic equations including director reorientation, fluid flow, and temperature redistribution across the HALC cavity. Calculations show that only under the influence of ∇T does the initially quiescent HALC sample settle down to a stationary flow regime with horizontal component of velocity ueq(r). The effects of ∇T and of the size of the HALC cavity on magnitude and direction of ueq(r) have been investigated for a number of hydrodynamic regimes. Calculations also showed that E influences only the director redistribution across the HALC but not the magnitude of the velocity ueq(r).

  11. Liquid crystal-on-organic field-effect transistor sensory devices for perceptive sensing of ultralow intensity gas flow touch.

    PubMed

    Seo, Jooyeok; Park, Soohyeong; Nam, Sungho; Kim, Hwajeong; Kim, Youngkyoo

    2013-01-01

    We demonstrate liquid crystal-on-organic field-effect transistor (LC-on-OFET) sensory devices that can perceptively sense ultralow level gas flows. The LC-on-OFET devices were fabricated by mounting LC molecules (4-cyano-4'-pentylbiphenyl - 5CB) on the polymer channel layer of OFET. Results showed that the presence of LC molecules on the channel layer resulted in enhanced drain currents due to a strong dipole effect of LC molecules. Upon applying low intensity nitrogen gas flows, the drain current was sensitively increased depending on the intensity and time of nitrogen flows. The present LC-on-OFET devices could detect extremely low level nitrogen flows (0.7 sccm-11 μl/s), which could not be felt by human skins, thanks to a synergy effect between collective behavior of LC molecules and charge-sensitive channel layer of OFET. The similar sensation was also achieved using the LC-on-OFET devices with a polymer film skin, suggesting viable practical applications of the present LC-on-OFET sensory devices. PMID:23948946

  12. Liquid Crystal-on-Organic Field-Effect Transistor Sensory Devices for Perceptive Sensing of Ultralow Intensity Gas Flow Touch

    NASA Astrophysics Data System (ADS)

    Seo, Jooyeok; Park, Soohyeong; Nam, Sungho; Kim, Hwajeong; Kim, Youngkyoo

    2013-08-01

    We demonstrate liquid crystal-on-organic field-effect transistor (LC-on-OFET) sensory devices that can perceptively sense ultralow level gas flows. The LC-on-OFET devices were fabricated by mounting LC molecules (4-cyano-4'-pentylbiphenyl - 5CB) on the polymer channel layer of OFET. Results showed that the presence of LC molecules on the channel layer resulted in enhanced drain currents due to a strong dipole effect of LC molecules. Upon applying low intensity nitrogen gas flows, the drain current was sensitively increased depending on the intensity and time of nitrogen flows. The present LC-on-OFET devices could detect extremely low level nitrogen flows (0.7 sccm-11 μl/s), which could not be felt by human skins, thanks to a synergy effect between collective behavior of LC molecules and charge-sensitive channel layer of OFET. The similar sensation was also achieved using the LC-on-OFET devices with a polymer film skin, suggesting viable practical applications of the present LC-on-OFET sensory devices.

  13. Liquid Crystal-on-Organic Field-Effect Transistor Sensory Devices for Perceptive Sensing of Ultralow Intensity Gas Flow Touch

    PubMed Central

    Seo, Jooyeok; Park, Soohyeong; Nam, Sungho; Kim, Hwajeong; Kim, Youngkyoo

    2013-01-01

    We demonstrate liquid crystal-on-organic field-effect transistor (LC-on-OFET) sensory devices that can perceptively sense ultralow level gas flows. The LC-on-OFET devices were fabricated by mounting LC molecules (4-cyano-4′-pentylbiphenyl – 5CB) on the polymer channel layer of OFET. Results showed that the presence of LC molecules on the channel layer resulted in enhanced drain currents due to a strong dipole effect of LC molecules. Upon applying low intensity nitrogen gas flows, the drain current was sensitively increased depending on the intensity and time of nitrogen flows. The present LC-on-OFET devices could detect extremely low level nitrogen flows (0.7 sccm–11 μl/s), which could not be felt by human skins, thanks to a synergy effect between collective behavior of LC molecules and charge-sensitive channel layer of OFET. The similar sensation was also achieved using the LC-on-OFET devices with a polymer film skin, suggesting viable practical applications of the present LC-on-OFET sensory devices. PMID:23948946

  14. Pauli-limiting effects in the upper critical fields of a clean LiFeAs single crystal

    NASA Astrophysics Data System (ADS)

    Khim, Seunghyun; Lee, Bumsung; Kim, Jae Wook; Choi, Eun Sang; Stewart, G. R.; Kim, Kee Hoon

    2011-09-01

    We have investigated the temperature dependence of the upper critical field Hc2(T ) in a LiFeAs single crystal by direct measurements of resistivity under static magnetic fields up to 36 T. We find in the case of a magnetic field H along the ab plane that Hc2ab(0) = 30 T is clearly lower than the orbital limiting field Hc2orb,ab(0) = 39.6 T estimated by the |dHc2ab/dT |Tc, suggesting the presence of both Pauli- and orbital-limiting effects in the pair breaking process. The best fit of Hc2ab(T ) to the Werthamer-Helfand-Hohenberg formula results in the Maki parameter α = 0.9 and negligible spin-orbit scattering constant (λso = 0.0). On the other hand, for H along the c axis, Hc2c(T ) increases linearly down to our lowest temperature of 0.8 K, which can be explained by the multiband effects. The anisotropy ratio Hc2ab(T )/Hc2c(T ) is 3 near Tc and systematically decreases upon lowering temperature to become 1.3 at zero temperature. A comparative overview of the behavior of Hc2ab(T ) in various Fe-based superconductors shows that, similar to LiFeAs, the calculated Hc2orb,ab(0) is generally much larger than the measured Hc2ab(0) and thus finite α values ranging from ˜0.4 to 3 are necessary to describe the low temperature Hc2ab(T ) behaviors. Moreover, LiFeAs is found to have the smallest |dHc2ab/dT |Tc values, indicating that LiFeAs is one of the cleanest Fe-based superconductors with a finite Maki parameter. We also discuss the implications of multiband effects and spin-orbit scattering based on the finding that the estimated Pauli-limiting field is generally much larger than the BCS prediction in the Fe-based superconductors.

  15. The Effect of Dissolved Side-Group Polymers on Pattern Dynamics in Nematic Liquid Crystals in a Rotating Magnetic Field

    NASA Astrophysics Data System (ADS)

    Pashkovsky, E. E.; Stille, W.; Strobl, G.; Talebi, D.

    1997-05-01

    Patterns formed by inversion walls in nematic layers exposed to a rotating magnetic field were studied. Dilute solutions of a mesogenic side group polymethacrylate in a low molecular weight liquid crystal (5CB) were used in comparison with the pure solvent. As found in a previous work, in this system the intensity of backflow (fluid flow induced by director rotation) can be controlled by the polymer concentration due to a specific increase of shear viscosity coefficients. In the synchronous regime of director rotation no significant effects of backflow on the dynamics of the walls are observed. Dynamic solitons known from the synchronous regime were also found at asynchronous rotation, when soliton lattices are formed by continuous nucleation. Here comparison with theory for given values of the lattice period shows soliton currents significantly reduced by backflow. Two of the three additional pattern forming states exclusively found at asynchronous rotation were completely suppressed in solutions with sufficient polymer concentration. The third of these states is affected by backflow in the growth rate of its patterns. Numerical calculations were performed to explain behavior of the patterns in the asynchronous state. For pure 5CB a quantitative comparison with the experiment was possible.

  16. Nonlinear elastic effects in phase field crystal and amplitude equations: Comparison to ab initio simulations of bcc metals and graphene

    NASA Astrophysics Data System (ADS)

    Hüter, Claas; Friák, Martin; Weikamp, Marc; Neugebauer, Jörg; Goldenfeld, Nigel; Svendsen, Bob; Spatschek, Robert

    2016-06-01

    We investigate nonlinear elastic deformations in the phase field crystal model and derived amplitude equation formulations. Two sources of nonlinearity are found, one of them is based on geometric nonlinearity expressed through a finite strain tensor. This strain tensor is based on the inverse right Cauchy-Green deformation tensor and correctly describes the strain dependence of the stiffness for anisotropic and isotropic behavior. In isotropic one- and two-dimensional situations, the elastic energy can be expressed equivalently through the left deformation tensor. The predicted isotropic low-temperature nonlinear elastic effects are directly related to the Birch-Murnaghan equation of state with bulk modulus derivative K'=4 for bcc. A two-dimensional generalization suggests K2D '=5 . These predictions are in agreement with ab initio results for large strain bulk deformations of various bcc elements and graphene. Physical nonlinearity arises if the strain dependence of the density wave amplitudes is taken into account and leads to elastic weakening. For anisotropic deformation, the magnitudes of the amplitudes depend on their relative orientation to the applied strain.

  17. Precise Characterisation of Molecular Orientation in a Single Crystal Field-Effect Transistor Using Polarised Raman Spectroscopy.

    PubMed

    Wood, Sebastian; Rigas, Grigorios-Panagiotis; Zoladek-Lemanczyk, Alina; Blakesley, James C; Georgakopoulos, Stamatis; Mas-Torrent, Marta; Shkunov, Maxim; Castro, Fernando A

    2016-01-01

    Charge transport in organic semiconductors is strongly dependent on the molecular orientation and packing, such that manipulation of this molecular packing is a proven technique for enhancing the charge mobility in organic transistors. However, quantitative measurements of molecular orientation in micrometre-scale structures are experimentally challenging. Several research groups have suggested polarised Raman spectroscopy as a suitable technique for these measurements and have been able to partially characterise molecular orientations using one or two orientation parameters. Here we demonstrate a new approach that allows quantitative measurements of molecular orientations in terms of three parameters, offering the complete characterisation of a three-dimensional orientation. We apply this new method to organic semiconductor molecules in a single crystal field-effect transistor in order to correlate the measured orientation with charge carrier mobility measurements. This approach offers the opportunity for micrometre resolution (diffraction limited) spatial mapping of molecular orientation using bench-top apparatus, enabling a rational approach towards controlling this orientation to achieve optimum device performance. PMID:27619423

  18. Simultaneous monitoring of protein adsorption kinetics using a quartz crystal microbalance and field-effect transistor integrated device.

    PubMed

    Goda, Tatsuro; Maeda, Yasuhiro; Miyahara, Yuji

    2012-09-01

    We developed an integrated device comprising a quartz crystal microbalance (QCM) and a field-effect transistor (FET) with a single common gold electrode in a flow chamber. An alternating current inducing oscillations in the piezoelectric quartz of the QCM sensor is electrically independent of the circuit for the FET output so that the two sensors in different detection mechanisms simultaneously record binding kinetics from a single protein solution on the same electrode. A conjunction of adsorbed mass from QCM with electric nature of bound protein from FET provided deeper understanding on a complex process of nonspecific protein adsorption and subsequent conformational changes at a solid/liquid interface. Lower apparent k(on) values obtained by FET than those obtained by QCM on hydrophobic surfaces are interpreted as preferred binding of protein molecules facing uncharged domains to the electrode surface, whereas higher k(off) values by FET than those by QCM imply active macromolecular rearrangements on the surfaces mainly driven by hydrophobic association in an aqueous medium. The advanced features of the combined sensor including in situ, label-free, and real-time monitoring provide information on structural dynamics, beyond measurements of affinities and kinetics in biological binding reactions. PMID:22861174

  19. Electronic transport within a quasi-two-dimensional model for rubrene single-crystal field effect transistors

    NASA Astrophysics Data System (ADS)

    Gargiulo, F.; Perroni, C. A.; Ramaglia, V. Marigliano; Cataudella, V.

    2011-12-01

    Spectral and transport properties of the quasi-two-dimensional adiabatic Su-Schrieffer-Heeger model are studied, adjusting the parameters in order to model rubrene single-crystal field effect transistors with small but finite density of injected charge carriers. We show that, with increasing temperature T, the chemical potential moves into the tail of the density of states corresponding to localized states, but this is not enough to drive the system into an insulating state. The mobility along different crystallographic directions is calculated, including vertex corrections that give rise to a transport lifetime one order of magnitude smaller than the spectral lifetime of the states involved in the transport mechanism. With increasing temperature, the transport properties reach the Ioffe-Regel limit, which is ascribed to less and less appreciable contribution of itinerant states to the conduction process. The model provides features of the mobility in close agreement with experiments: right order of magnitude, scaling as a power law T-γ (with γ close or larger than two), and correct anisotropy ratio between different in-plane directions. Due to a realistic high-dimensional model, the results are not biased by uncontrolled approximations.

  20. Amplified Emission and Field-Effect Transistor Characteristics of One-Dimensionally Structured 2,5-Bis(4-biphenylyl)thiophene Crystals.

    PubMed

    Hashimoto, Kazumasa; Sasaki, Fumio; Hotta, Shu; Yanagi, Hisao

    2016-04-01

    One-dimensional (1D) structures of 2,5-bis(4-biphenylyl)thiophene (BP1T) crystals are fabricated for light amplification and field-effect transistor (FET) measurements. A strip-shaped 1D structure (10 µm width) made by photolitography of a vapor-deposited polycrystalline film shows amplified spontaneous emission and lasing oscillations under optical pumping. An FET fabricated with this 1D structure exhibits hole-conduction with a mobility of µh = 8.0 x 10(-3) cm2/Vs. Another 1 D-structured FET is fabricated with epitaxially grown needle-like crystals of BP1T. This needle-crystal FET exhibits higher mobility of µh = 0.34 cm2/Vs. This improved hole mobility is attributed to the single-crystal channel of epitaxial needles while the grain boudaries in the polycrystalline 1 D-structure decrease the carrier transport. PMID:27451604

  1. Local Field Modulation Induced Three-Order Upconversion Enhancement: Combining Surface Plasmon Effect and Photonic Crystal Effect.

    PubMed

    Yin, Ze; Li, Hang; Xu, Wen; Cui, Shaobo; Zhou, Donglei; Chen, Xu; Zhu, Yongsheng; Qin, Guanshi; Song, Hongwei

    2016-04-01

    A 2D surface plasmon photonic crystal (SPPC) is achieved by implanting gold nanorods onto the periodic surface apertures of the poly(methyl methacrylate) (PMMA) opal photonic crystals. On the surface of the SPPC, the overall upconversion luminescence intensity of NaYF4 :Yb(3+) , Er(3+) under 980 nm excitation is improved more than 10(3) fold. The device is easily shifted to a transparent flexible substrate, applied to flexible displays. PMID:26833556

  2. Effect of external electric field and background illumination on the intensity distribution of optical surface waves in the metal – photorefractive crystal system

    SciTech Connect

    Akhmedzhanov, I M

    2013-11-30

    The influence of the external electric field and background illumination on the intensity distribution of optical photorefractive surface waves at the metal – photorefractive crystal interface has been numerically simulated. The simulation is performed for a strontium – barium niobate (SBN) crystal using the parameters corresponding to the experimental data. The replacement of a real metal with an ideal one and the choice of the corresponding boundary conditions (depending on the wave power) in the numerical simulation have been substantiated. The calculation results have shown good agreement with the previously published experimental data on the effect of background illumination and a significant discrepancy for the data on the effect of the external electric field. It is found that the effect of the external electric field can be significantly enhanced by reducing the optical power of the photorefractive wave to values close to the threshold ones. (nonlinear optical phenomena)

  3. Crystallization of insulin and lysozyme under reduced convection condition in a large gradient magnetic field

    NASA Astrophysics Data System (ADS)

    Yin, D. C.; Wakayama, N. I.; Fujiwara, M.; Harata, K.; Xue, X. P.; Fu, Z. X.; Zhang, S. W.; Shang, P.; Tanimoto, Y.

    The crystallization of protein from solution is governed by the process of transport phenomenon Any reason affecting the process of solute transport will impose effects on the crystallization process thus further affects the crystal quality Recent advancement in superconducting magnet technology makes it possible to provide a low cost long-time durable low effective gravity environment for the control of convection which is similar to the environment in the space As an ideal means to damp natural convection in a non-conductive solution on the Earth it may find applications in the field of protein crystallization In this presentation the authors investigated the crystallization of orthorhombic lysozyme crystals tetragonal lysozyme crystals and insulin crystals in a large gradient magnetic field Three effective gravity levels were used milli-gravity around 0G normal gravity 1G and hypergravity 1 8G Comparisons of the crystal quality obtained inside and outside the magnetic field showed that both the magnetic field and the effective gravity could affect the crystal quality But the effect also depends on the crystal and protein type For lysozyme crystals in tetragonal form the magnetic field and effective gravity showed no obvious effect on the quality whereas for the crystals in orthorhombic form both the magnetic field and effective gravity improved the crystal quality For insulin crystal which is highly symmetrical magnetic field and effective gravity showed no strong effect on the crystal quality It is well known that

  4. Effect of a High Magnetic Field on Microstructures of Ni-Based Single Crystal Superalloy During Seed Melt-Back

    NASA Astrophysics Data System (ADS)

    Xuan, Weidong; Liu, Huan; Li, Chuanjun; Ren, Zhongming; Zhong, Yunbo; Li, Xi; Cao, Guanghui

    2016-04-01

    The effects of a high magnetic field on microstructures during seed melt-back of superalloy were investigated. Experimental results indicated that the high magnetic field significantly modified the melt-back interface shape and the melt-back zone length. In addition, stray grain on the edge of sample was effectively suppressed in the high magnetic field. Based on experimental results and quantitative analysis, the above results should be attributed to the increasing temperature gradient in a high magnetic field.

  5. Crystal growth under external electric fields

    SciTech Connect

    Uda, Satoshi; Koizumi, Haruhiko; Nozawa, Jun; Fujiwara, Kozo

    2014-10-06

    This is a review article concerning the crystal growth under external electric fields that has been studied in our lab for the past 10 years. An external field is applied electrostatically either through an electrically insulating phase or a direct injection of an electric current to the solid-interface-liquid. The former changes the chemical potential of both solid and liquid and controls the phase relationship while the latter modifies the transport and partitioning of ionic solutes in the oxide melt during crystallization and changes the solute distribution in the crystal.

  6. Grain boundary barrier modification due to coupling effect of crystal polar field and water molecular dipole in ZnO-based structures

    SciTech Connect

    Ji, Xu; Zhu, Yuan E-mail: phzktang@ust.hk; Chen, Mingming; Su, Longxing; Chen, Anqi; Zhao, Chengchun; Gui, Xuchun; Xiang, Rong; Huang, Feng; Tang, Zikang E-mail: phzktang@ust.hk

    2014-06-16

    Surface water molecules induced grain boundaries (GBs) barrier modification was investigated in ZnO and ZnMgO/ZnO films. Tunable electronic transport properties of the samples by water were characterized via a field effect transistor (FET) device structure. The FETs fabricated from polar C-plane ZnO and ZnMgO/ZnO films that have lots of GBs exhibited obvious double Schottky-like current-voltage property, whereas that fabricated from nonpolar M-plane samples with GBs and ZnO bulk single-crystal had no obvious conduction modulation effects. Physically, these hallmark properties are supposed to be caused by the electrostatical coupling effect of crystal polar field and molecular dipole on GBs barrier.

  7. Magnetic Field Induced Phase Transitions in Gd5(Si1.95Ge2.05)Single Crystal and the Anisotropic Magnetocaloric Effect

    SciTech Connect

    H. Tang; V.K. Pecharsky; A.O. Pecharsky; D.L. Schlagel; T.A. Lograsso; K.A. Gschneidner,jr.

    2004-09-30

    The magnetization measurements using a Gd{sub 5}(Si{sub 1.95}Ge{sub 2.05}) single crystal with the magnetic field applied along three crystallographic directions, [001], [010] and [100], were carried out as function of applied field (0-56 kOe) at various temperatures ({approx}5-320 K). The magnetic-field induced phase transformations at temperature above the zero-field critical temperature, i.e. the paramagnetic (PM) {leftrightarrow} ferromagnetic (FM) transitions with application or removal of magnetic field, are found to be temperature dependent and hysteretic. The corresponding critical fields increase with increasing temperature. The magnetic field (H)-temperature (T) phase diagrams have been constructed for the Gd{sub 5}(Si{sub 1.95}Ge{sub 2.05}) single crystal with field along the three directions. A small anisotropy has been observed. The magnetocaloric effect (MCE) has been calculated from the isothermal magnetization data, and the observed anisotropy correlates with H-T phase diagrams. The results are discussed in connection with the magnetic-field induced martensitic-like structural transition observed in the Gd{sub 5}(Si{sub 2}Ge{sub 2})-type compounds.

  8. Magnetic measurements on Pr (BrO3)3 ṡ 9H2O single crystal and a study of the effects and origin of the crystal field

    NASA Astrophysics Data System (ADS)

    Neogy, D.; Purohit, T.; Chatterji, A.

    1986-02-01

    Praseodymium bromate was prepared from Pr2O3 and the single crystals of Pr (BrO3)3 ṡ 9H2O were grown. The principal magnetic susceptibility χ⊥ and the anisotropy χ∥-χ⊥ was measured in the range 300-90 K. The variation of the average magnetic moment peff with temperature is appreciable showing a deviation from the Curie law. The magnetic anistropy χ∥-χ⊥ is found to be much higher than in Pr-ethylsulfate where the Pr3+ ion occupies a site very similar to that in PrBR. A crystal field analysis with a field of D3h symmetry is found to provide an excellent account of the magnetic properties observed by us and Simizu et al. [J. Appl. Phys. 55, 2333 (1984)] from 300 K down to ˜0.06 K. The Hamiltonian was diagonalized in the complete basis of the 3H ground term taking care of the intermediate coupling effects to a large extent. Some important predictions on the electronic heat capacity and the electric quadrupole splitting have been made. An estimate of the crystal field parameters has been made using the available structural data on the crystal and the results are discussed in the light of our phenomenological set of parameters.

  9. Crystal growth under microgravity conditions with using of magnetic fields

    NASA Astrophysics Data System (ADS)

    Feonychev, A.; Bondareva, N.

    The peculiarities of melt flows and crystal growth by the Bridgman and floating zone methods aboard spacecrafts under the action of steady axial or rotating magnetic field are considered. Steady magnetic field can minimize adverse effect of residual accelerations and vibrations on dopant segregation in crystals growing by the Bridgman method but it requires using strong magnetic fields, which induces specific oscillations. Under strong convection in terrestrial conditions steady magnetic field gives positive effect. Under growth of small-sized crystals by the floating zone method in microgravity conditions an use of steady magnetic field brings into dramatic increase of radial segregation due to convective vortex to free fluid surface. The flows being created by rotating magnetic field and resultant under combination of Marangoni convection with rotating magnetic field were studied for wide range of parameters including the regimes of oscillatory (turbulent) convection. Mathematical model and computer program was tested by published results of two experiments. The dependence of transition from laminar to oscillatory flow was obtained for different boundary conditions, geometric parameters of fluid and intensity of magnetic field. Specific oscillations with very low frequency and oscillations of the beating type had been discovered under the action rotating magnetic field on Marangoni convection. The mutual influence of rotating magnetic field and thermocapillary convection on flow stability was noted. Use of rotating magnetic field under crystal growth by floating zone method leads to reduction of azimuth velocity which is responsible for origin of oscillatory convection and striation of crystals. It was shown on concrete examples that there is a possibility to reduce radial segregation under optimization of rotating velocity and intensity of magnetic field. For the Bridgman method (in general for ampoule methods of crystal growth), the use of rotating magnetic

  10. Effects of composition and temperature on the large field behavior of [011]{sub C} relaxor ferroelectric single crystals

    SciTech Connect

    Gallagher, John A.; Lynch, Christopher S.; Tian, Jian

    2014-08-04

    The large field behavior of [011]{sub C} cut relaxor ferroelectric lead indium niobate–lead magnesium niobate–lead titanate, xPb(In{sub 1/2}Nb{sub 1/2})O{sub 3}-(1-x-y)Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}-yPbTiO{sub 3}, single crystals was experimentally characterized in the piezoelectric d{sub 322}-mode configuration under combined mechanical, electrical, and thermal loading. Increasing the concentration of lead indium niobate and decreasing the concentration of lead titanate in compositions near the morphotropic phase boundary resulted in a decrease of mechanical compliance, dielectric permittivity, and piezoelectric coefficients as well as a shift from a continuous to a discontinuous transformation.

  11. Effect of surface anchoring energy on electro-optic characteristics of a fringe-field switching liquid crystal cell

    NASA Astrophysics Data System (ADS)

    Kim, Jin Hyun; Kang, Wan Seok; Sol Choi, Han; Park, Kiwoong; Lee, Joong Hee; Yoon, Sangho; Yoon, Sukin; Lee, Gi-Dong; Lee, Seung Hee

    2015-11-01

    Surface anchoring strength of the alignment layer on liquid crystal (LC) determines electro-optic characteristics in the LC devices. This paper investigates how azimuthal and polar anchoring strength affects the electro-optic performance of a fringe-field switching (FFS) mode associated with electrode structure, cell gap and dielectric anisotropy of the LC by numerical simulation. Our important findings in the FFS mode are that both azimuthal and polar anchoring energy can considerably affect the operating voltage and also maximum transmittance when using a LC with positive dielectric anisotropy; however, when using a LC with negative dielectric anisotropy only azimuthal anchoring energy affects electro-optic characteristics. The study proposes an optimal design of an alignment layer for maximizing transmittance in the FFS mode.

  12. Fluorination of Metal Phthalocyanines: Single-Crystal Growth, Efficient N-Channel Organic Field-Effect Transistors, and Structure-Property Relationships

    NASA Astrophysics Data System (ADS)

    Jiang, Hui; Ye, Jun; Hu, Peng; Wei, Fengxia; Du, Kezhao; Wang, Ning; Ba, Te; Feng, Shuanglong; Kloc, Christian

    2014-12-01

    The fluorination of p-type metal phthalocyanines produces n-type semiconductors, allowing the design of organic electronic circuits that contain inexpensive heterojunctions made from chemically and thermally stable p- and n-type organic semiconductors. For the evaluation of close to intrinsic transport properties, high-quality centimeter-sized single crystals of F16CuPc, F16CoPc and F16ZnPc have been grown. New crystal structures of F16CuPc, F16CoPc and F16ZnPc have been determined. Organic single-crystal field-effect transistors have been fabricated to study the effects of the central metal atom on their charge transport properties. The F16ZnPc has the highest electron mobility (~1.1 cm2 V-1 s-1). Theoretical calculations indicate that the crystal structure and electronic structure of the central metal atom determine the transport properties of fluorinated metal phthalocyanines.

  13. Fluorination of Metal Phthalocyanines: Single-Crystal Growth, Efficient N-Channel Organic Field-Effect Transistors, and Structure-Property Relationships

    PubMed Central

    Jiang, Hui; Ye, Jun; Hu, Peng; Wei, Fengxia; Du, Kezhao; Wang, Ning; Ba, Te; Feng, Shuanglong; Kloc, Christian

    2014-01-01

    The fluorination of p-type metal phthalocyanines produces n-type semiconductors, allowing the design of organic electronic circuits that contain inexpensive heterojunctions made from chemically and thermally stable p- and n-type organic semiconductors. For the evaluation of close to intrinsic transport properties, high-quality centimeter-sized single crystals of F16CuPc, F16CoPc and F16ZnPc have been grown. New crystal structures of F16CuPc, F16CoPc and F16ZnPc have been determined. Organic single-crystal field-effect transistors have been fabricated to study the effects of the central metal atom on their charge transport properties. The F16ZnPc has the highest electron mobility (~1.1 cm2 V−1 s−1). Theoretical calculations indicate that the crystal structure and electronic structure of the central metal atom determine the transport properties of fluorinated metal phthalocyanines. PMID:25524460

  14. The effect of an electric field on the morphological stability of the crystal-melt interface of a binary alloy. III - Weakly nonlinear theory

    NASA Technical Reports Server (NTRS)

    Wheeler, A. A.; Mcfadden, G. B.; Coriell, S. R.; Hurle, D. T. J.

    1990-01-01

    The effect of a constant electric current on the crystal-melt interface morphology during directional solidification at constant velocity of a binary alloy is considered. A linear temperature field is assumed, and thermoelectric effects and Joule heating are neglected; electromigration and differing electrical conductivities of crystal and melt are taken into account. A two-dimensional weakly nonlinear analysis is carried out to third order in the interface amplitude, resulting in a cubic amplitude equation that describes whether the bifurcation from the planar state is supercritical or subcritical. For wavelengths corresponding to the most dangerous mode of linear theory, the demarcation between supercritical and subcritical behavior is calculated as a function of processing conditions and material parameters. The bifurcation behavior is a sensitive function of the magnitude and direction of the electric current and of the electrical conductivity ratio.

  15. Observation of high field DHVA-effect and induced magnetism in single crystal TiBe/sub 2/

    SciTech Connect

    van Deursen, A.P.J.; van Ruitenbeek, J.M.; Verhoef, W.A.; de Vroomen, A.R.; Smith, J.L.; de Groot, R.A.; Koelling, D.D.; Mueller, F.M.

    1981-01-01

    Recently much interest has been given to itinerant magnetism in cubic Laves phase or C15 materials. Primarily this stems from the discussion of the relationship of p-state pairing and ferromagnetism in ZrZn/sub 2/ by Enz and Matthias, and the possibility of triplet superconductivity. The most recent work in this field has focused on the isoelectronic, isostructural material TiBe/sub 2/, and the possibility that this material is metamagnetic. That TiBe/sub 2/ is close to some form of magnetic instability can be infered indirectly from the peaked nature of its density of states near the fermi level, but also from the observation of ferromagnetism in TiBe/sub 2-x/Cu/sub x/, when x is greater than about 0.15. In this paper a single crystal of pure TiBe/sub 2/ is considered in fields larger than 15 Tesla (T) and at a temperature of 1.3/sup 0/K.

  16. Statistical electric field and switching time distributions in PZT 1Nb2Sr ceramics: Crystal- and microstructure effects

    NASA Astrophysics Data System (ADS)

    Zhukov, Sergey; Kungl, Hans; Genenko, Yuri A.; von Seggern, Heinz

    2014-01-01

    Dispersive polarization response of ferroelectric PZT ceramics is analyzed assuming the inhomogeneous field mechanism of polarization switching. In terms of this model, the local polarization switching proceeds according to the Kolmogorov-Avrami-Ishibashi scenario with the switching time determined by the local electric field. As a result, the total polarization reversal is dominated by the statistical distribution of the local field magnitudes. Microscopic parameters of this model (the high-field switching time and the activation field) as well as the statistical field and consequent switching time distributions due to disorder at a mesoscopic scale can be directly determined from a set of experiments measuring the time dependence of the total polarization switching, when applying electric fields of different magnitudes. PZT 1Nb2Sr ceramics with Zr/Ti ratios 51.5/48.5, 52.25/47.75, and 60/40 with four different grain sizes each were analyzed following this approach. Pronounced differences of field and switching time distributions were found depending on the Zr/Ti ratios. Varying grain size also affects polarization reversal parameters, but in another way. The field distributions remain almost constant with grain size whereas switching times and activation field tend to decrease with increasing grain size. The quantitative changes of the latter parameters with grain size are very different depending on composition. The origin of the effects on the field and switching time distributions are related to differences in structural and microstructural characteristics of the materials and are discussed with respect to the hysteresis loops observed under bipolar electrical cycling.

  17. Unifying the crystallization behavior of hexagonal and square crystals with the phase-field-crystal model

    NASA Astrophysics Data System (ADS)

    Tao, Yang; Zheng, Chen; Jing, Zhang; Yongxin, Wang; Yanli, Lu

    2016-03-01

    By employing the phase-field-crystal models, the atomic crystallization process of hexagonal and square crystals is investigated with the emphasis on the growth mechanism and morphological change. A unified regime describing the crystallization behavior of both crystals is obtained with the thermodynamic driving force varying. By increasing the driving force, both crystals (in the steady-state) transform from a faceted polygon to an apex-bulged polygon, and then into a symmetric dendrite. For the faceted polygon, the interface advances by a layer-by-layer (LL) mode while for the apex-bulged polygonal and the dendritic crystals, it first adopts the LL mode and then transits into the multi-layer (ML) mode in the later stage. In particular, a shift of the nucleation sites from the face center to the area around the crystal tips is detected in the early growth stage of both crystals and is rationalized in terms of the relation between the crystal size and the driving force distribution. Finally, a parameter characterizing the complex shape change of square crystal is introduced. Project supported by the National Natural Science Foundation of China (Grant Nos. 54175378, 51474176, and 51274167), the Natural Science Foundation of Shaanxi Province, China (Grant No. 2014JM7261), and the Doctoral Foundation Program of Ministry of China (Grant No. 20136102120021).

  18. Magnetic properties of Ce{sup 3+} in Pb{sub 1{minus}x}Ce{sub x}Se: Kondo and crystal-field effect

    SciTech Connect

    Gratens, X.; Charar, S.; Averous, M.; Isber, S.; Deportes, J.; Golacki, Z.

    1997-10-01

    Electron paramagnetic resonance (EPR) experiments were performed on a Pb{sub 1{minus}x}Ce{sub x}Se crystal at liquid-helium temperatures and show very clearly that the doublet {Gamma}{sub 7} is the ground state for cerium ions. The cubic symmetry is shown and the effective Land{acute e} factor for the Ce{sup 3+} is determined to be 1.354{plus_minus}0.003. An orbital reduction factor is introduced to explain the g experimental value. High-field magnetization results are in good agreement with the EPR results. The nominal Ce composition in PbSe deduced from saturation of the magnetization, x=0.0405{plus_minus}0.0003, is very closed to the value determined by microprobe analysis (x=0.04). At 1.5 K, an antiferromagnetic interaction between the nearest-neighbor cerium atoms is found, J{sub ex}/k{sub B}={minus}0.715thinspK. The low-field magnetic-susceptibility results show that the magnetic moment of cerium impurities is strongly temperature dependent, explained by the presence of the crystal-field effect and the Kondo effect. {copyright} {ital 1997} {ital The American Physical Society}

  19. Birefringence of the antiferromagnetic crystals linear in a magnetic field

    NASA Astrophysics Data System (ADS)

    Eremenko, V. V.; Kharchenko, N. F.; Beliy, L. I.; Tutakina, O. P.

    1980-01-01

    The new linear magneto-optical effect-birefringence-of a linear polarized light which is directly proportional to the magnetic field strength has been observed. This effect is permitted in crystals which allow piezo-magnetic properties. One was studied in antiferromagnet CoF 2 and CoCO 3 for the longitudinal geometry of an experiment.

  20. Electric-field-assisted convective assembly of colloidal crystal coatings.

    PubMed

    Kleinert, Jairus; Kim, Sejong; Velev, Orlin D

    2010-06-15

    A new technique that combines evaporative convective deposition of colloidal crystal coatings with an electric field to achieve more rapid assembly and reduce the defects in the crystal structure is reported. When an ac voltage is applied across the particle suspension and the substrate in the convective assembly process, a longer film spreads from the meniscus by the electrowetting-on-dielectric (EWOD) effect. The data suggest that the EWOD-increased liquid surface area results in increased evaporation-driven particle flux and crystal assembly that is up to five times more rapid. The extended drying film also provides more time for particle rearrangement before the structure becomes fixed, resulting in formation of crystal domains an order of magnitude larger than those deposited by convective assembly alone. The results demonstrate that EWOD is a facile tool for controlling particle assembly processes in wetting films. The technique could be used in improved large-scale colloidal crystal coating processes. PMID:20465234

  1. Consistent Hydrodynamics for Phase Field Crystals.

    PubMed

    Heinonen, V; Achim, C V; Kosterlitz, J M; Ying, See-Chen; Lowengrub, J; Ala-Nissila, T

    2016-01-15

    We use the amplitude expansion in the phase field crystal framework to formulate an approach where the fields describing the microscopic structure of the material are coupled to a hydrodynamic velocity field. The model is shown to reduce to the well-known macroscopic theories in appropriate limits, including compressible Navier-Stokes and wave equations. Moreover, we show that the dynamics proposed allows for long wavelength phonon modes and demonstrate the theory numerically showing that the elastic excitations in the system are relaxed through phonon emission. PMID:26824543

  2. Phase-Field Simulations of Crystal Growth

    NASA Astrophysics Data System (ADS)

    Plapp, Mathis

    2010-07-01

    This course gives an elementary introduction to the phase-field method and to its applications for the modeling of crystal growth. Two different interpretations of the phase-field variable are given and discussed. It can be seen as a physical order parameter that characterizes a phase transition, or as a smoothed indicator function that tracks domain boundaries. Elementary phase-field models for solidification and epitaxial growth are presented and are applied to the dendritic growth of a pure substance and the step-flow growth on a vicinal surface.

  3. Effect of an applied electric field on a weakly anchored non-planar Nematic Liquid Crystal (NLC) layer

    NASA Astrophysics Data System (ADS)

    Mema, Ensela; Cummings, Linda J.; Kondic, Lou

    We consider a mathematical model that consists of a NLC layer sandwiched between two parallel bounding plates, across which an external field is applied. We investigate its effect on the director orientation by considering the dielectric and flexoelectric contributions and varying parameters that represent the anchoring conditions and the electric field strength. In particular, we investigate possible director configurations that occur in weakly anchored and non-planar systems. We observe that non-planar anchoring angles destroy any hysteresis seen in a planar system by eliminating the fully vertical director configuration and the ''saturation threshold'' seen in weakly anchored planar Freedericksz cells. Supported by NSF Grant No. DMS-1211713.

  4. Electric field induced biaxiality and the electro-optic effect in a bent-core nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Nagaraj, Mamatha; Panarin, Y. P.; Manna, U.; Vij, J. K.; Keith, C.; Tschierske, C.

    2010-01-01

    We report the observation of a biaxial nematic phase in a bent-core molecular system using polarizing microscopy, electro-optics, and dielectric spectroscopy, where we find that the biaxiality exists on a microscopic scale. An application of electric field induces a macroscopic biaxiality and in consequence gives rise to electro-optic switching. This electro-optic effect shows significant potential in applications for displays due to its fast high-contrast response. The observed electro-optic switching is explained in terms of the interaction of the ferroelectric clusters with the electric field.

  5. Entropy change of a Ni45.5Co4.5Mn37In13 single crystal studied by scanning calorimetry in high magnetic fields: Field dependence of the magnetocaloric effect

    NASA Astrophysics Data System (ADS)

    Bourgault, D.; Porcar, L.; Rivoirard, S.; Courtois, P.; Hardy, V.

    2015-08-01

    By using differential scanning calorimetry, direct entropy variations have been recorded along the martensitic transformation of a Ni45.5Co4.5Mn37In13 single crystal in various magnetic fields. A large negative magnetocaloric effect associated to the transformation from virtually non-magnetic martensite to ferromagnetic austenite coexists with a weaker, positive effect related to the Curie transition in the latter phase. It is shown that the field-dependence of the maximum isothermal entropy change can be modelized by taking into account the interplay of both magnetocaloric contributions, as well as the intrinsic width of the martensitic transformation.

  6. Organic Memory Devices: 2D Mica Crystal as Electret in Organic Field-Effect Transistors for Multistate Memory (Adv. Mater. 19/2016).

    PubMed

    Zhang, Xiaotao; He, Yudong; Li, Rongjin; Dong, Huanli; Hu, Wenping

    2016-05-01

    R. Li, H. Dong, and co-workers describe the exfoliation of cheap and abundant minerals, such as mica, into nanometer-thick 2D crystals with atomically flat surfaces. As described on page 3755, the application of the 2D electret in organic field-effect transistors is well-suited for flexible nonvolatile memory devices. Stored information can be retrieved even after power cycling. Moreover, the devices can be used as full-function transistors with a low-resistance and a high-resistance state. PMID:27167032

  7. Anisotropy of the upper critical fields and the paramagnetic Meissner effect in La1.85Sr0.15CuO4 single crystals

    NASA Astrophysics Data System (ADS)

    Felner, I.; Tsindlekht, M. I.; Drachuck, G.; Keren, A.

    2013-02-01

    Optimally doped La1.85Sr0.15CuO4 single crystals have been investigated by dc and ac magnetic measurements. These crystals have rectangular needle-like shapes with the long needle axis parallel to the crystallographic c axis (c-crystal) or parallel to the basal planes (a-crystal). In both crystals, the temperature dependence of the upper critical fields (HC2) and the surface critical field (HC3) were measured. The H-T phase diagram is presented. Close to TC = 35 K, for the c-crystal, {\\boldsymbol{\\gamma}}^{c}={H}_{{C3}}^{c}/{H}_{{C2}}^{c}=1.8 0(2), whereas for the a-crystal the {\\boldsymbol{\\gamma}}^{a}={H}_{{C3}}^{a}/{H}_{{C2}}^{a}=4.0(2) obtained is much higher than 1.69, predicted by the ideal mathematical model. At low applied dc fields, positive field-cooled branches known as the ‘paramagnetic Meissner effect’ (PME) are observed; their magnitude is inversely proportional to H. The anisotropic PME is observed in both a- and c-crystals, only when the applied field is along the basal planes. It is speculated that the high γa and the PME are connected to each other.

  8. Magnetic ordering and crystal field effects in quasi-caged structure compound PrFe2Al8

    NASA Astrophysics Data System (ADS)

    Nair, Harikrishnan S.; Ghosh, Sarit K.; Ramesh Kumar, K.; Strydom, André M.

    2016-04-01

    The compound PrFe2Al8 possesses a three-dimensional network structure resulting from the packing of Al polyhedra centered at the transition metal element Fe and the rare earth Pr. Along the c-axis, Fe and Pr form chains which are separated from each other by the Al-network. In this paper, the magnetism and crystalline electric field effects in PrFe2Al8 are investigated through the analysis of magnetization and specific heat data. A magnetic phase transition in the Pr lattice is identified at TNPr ≈ 4 K in dc magnetization and ac susceptibility data. At 2 K, the magnetization isotherm presents a ferromagnetic saturation, however, failing to reach full spin-only ferromagnetic moment of Pr3+. Metamagnetic step-like low-field features are present in the magnetization curve at 2 K which is shown to shift upon field-cooling the material. Arrott plots centered around TPrN display "S"-like features suggestive of an inhomogeneous magnetic state. The magnetic entropy, Sm, estimated from specific heat outputs a value of R ln(2) at TN2 suggesting a doublet state for Pr3+. The magnetic specific heat is modeled by using a 9-level Schottky equation pertinent to the Pr3+ ion with J=4. Given the crystalline electric field situation of Pr3+, the inference of a doublet state from specific heat and consequent long-range magnetic order is an unexpected result.

  9. Realization of high-performance hetero-field-effect-transistor-type ultraviolet photosensors using p-type GaN comprising three-dimensional island crystals

    NASA Astrophysics Data System (ADS)

    Yamamoto, Yuma; Yoshikawa, Akira; Kusafuka, Toshiki; Okumura, Toshiki; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu

    2016-05-01

    High-performance AlGaN/AlGaN hetero-field-effect-transistor (HFET)-type photosensors with high photosensitivity were fabricated using p-type GaN comprising three-dimensional island crystals. The p-type GaN layers were grown on AlGaN layers at a high AlN molar fraction, and the area of p-type GaN comprising three-dimensional island crystals increased as the thickness of the p-type GaN film decreased, resulting in a reduced p-type GaN coverage ratio. The p-type GaN layers comprising three-dimensional island crystals and showing low coverage ratios were then used to fabricate HFET-type photosensors with high photosensitivity. A high light sensitivity of 1.5 × 104 A/W was obtained at a source–drain voltage (V SD) of 0.5 V for a photosensor with a p-type GaN thickness of 20 nm. Moreover, the dark current was suppressed to 10‑10 A/mm and the photosensor achieved an extremely high photocurrent to dark current density ratio.

  10. Ferromagnetic Switching of Knotted Vector Fields in Liquid Crystal Colloids.

    PubMed

    Zhang, Qiaoxuan; Ackerman, Paul J; Liu, Qingkun; Smalyukh, Ivan I

    2015-08-28

    We experimentally realize polydomain and monodomain chiral ferromagnetic liquid crystal colloids that exhibit solitonic and knotted vector field configurations. Formed by dispersions of ferromagnetic nanoplatelets in chiral nematic liquid crystals, these colloidal ferromagnets exhibit spontaneous long-range alignment of magnetic dipole moments of individual platelets, giving rise to a continuum of the magnetization field M(r). Competing effects of surface confinement and chirality prompt spontaneous formation and enable the optical generation of localized twisted solitonic structures with double-twist tubes and torus knots of M(r), which exhibit a strong sensitivity to the direction of weak magnetic fields ∼1  mT. Numerical modeling, implemented through free energy minimization to arrive at a field-dependent three-dimensional M(r), shows a good agreement with experiments and provides insights into the torus knot topology of observed field configurations and the corresponding physical underpinnings. PMID:26371682

  11. Nonequilibrium kinetics of the electron–phonon sybsystem of a crystal in a strong electric field as a base of the electroplastic effect

    SciTech Connect

    Karas, V. I. Vlasenko, A. M.; Sokolenko, V. I.; Zakharov, V. E.

    2015-09-15

    We present the results of a kinetic analysis of nonequilibrium dynamics of the electron–phonon system of a crystal in a strong electric field based on the proposed method of numerically solving a set of Boltzmann equations for electron and phonon distribution functions without expanding the electron distribution function into a series in the phonon energy. It is shown that the electric field action excites the electron subsystem, which by transferring energy to the phonon subsystem creates a large amount of short-wave phonons that effectively influence the lattice defects (point, lines, boundaries of different phases), which results in a redistribution of and decrease in the lattice defect density, in damage healing, in a decrease in the local peak stress, and a decrease in the degradation level of the construction material properties.

  12. The effect of magnetic field on bistability in 1D photonic crystal doped by magnetized plasma and coupled nonlinear defects

    SciTech Connect

    Mehdian, H.; Mohammadzahery, Z.; Hasanbeigi, A.

    2014-01-15

    In this work, we study the defect mode and bistability behavior of 1-D photonic band gap structure with magnetized plasma and coupled nonlinear defects. The transfer matrix method has been employed to investigate the magnetic field effect on defect mode frequency and bistability threshold. The obtained results show that the frequency of defect mode and bistability threshold can be altered, without changing the structure of the photonic multilayer. Therefore, the bistability behavior of the subjected structure in the presence of magnetized plasma can be utilized in manufacturing wide frequency range devices.

  13. Phase-Field Crystals with Elastic Interactions

    SciTech Connect

    Stefanovic, Peter; Provatas, Nikolas; Haataja, Mikko

    2006-06-09

    We report on a novel extension of the recently introduced phase-field crystal (PFC) method [Elder et al., Phys. Rev. Lett. 88, 245701 (2002)], which incorporates elastic interactions as well as crystal plasticity and diffusive dynamics. In our model, elastic interactions are mediated through wave modes that propagate on time scales many orders of magnitude slower than atomic vibrations but still much faster than diffusive time scales. This allows us to preserve the quintessential advantage of the PFC model: the ability to simulate atomic-scale interactions and dynamics on time scales many orders of magnitude longer than characteristic vibrational time scales. We demonstrate the two different modes of propagation in our model and show that simulations of grain growth and elastoplastic deformation are consistent with the microstructural properties of nanocrystals.

  14. Large scale pattern graphene electrode for high performance in transparent organic single crystal field-effect transistors.

    PubMed

    Liu, Wei; Jackson, Biyun Li; Zhu, Jing; Miao, Cong-Qin; Chung, Choong-Heui; Chung, Choon-Heui; Park, Young-Ju; Sun, Ke; Woo, Jason; Xie, Ya-Hong

    2010-07-27

    High quality, large grain size graphene on polycrystalline nickel film on two inch silicon wafers was successfully synthesized by the chemical vapor deposition (CVD) method. The polydimethylsiloxane (PDMS) stamping method was used for graphene transferring in this experiment. The graphene transferred onto Al2O3/ITO substrates was patterned into macroscopic dimension electrodes using conventional lithography followed by oxygen plasma etching. Experimental results show that this graphene can serve as transparent source and drain electrodes in high performance organic semiconductor nanoribbon organic field-effect transistors (OFETs), facilitating high hole injection efficiency due to the preferred work function match with the channel material: single crystalline copper phthalocyanine (CuPc) nanoribbons. The nanoribbons were grown on top of the patterned graphene via evaporate-deposition to form the FET device. The carrier mobility and on/off current ratio of such devices were measured to be as high as 0.36 cm2/(V s) and 10(4). PMID:20536162

  15. Magnetic-field tunable defect modes in a photonic-crystal/liquid-crystal cell.

    PubMed

    Zyryanov, Victor Ya; Myslivets, Sergey A; Gunyakov, Vladimir A; Parshin, Alexander M; Arkhipkin, Vasily G; Shabanov, Vasily F; Lee, Wei

    2010-01-18

    Light transmission spectrum of a multilayer photonic crystal with a central liquid-crystal defect layer placed between crossed polarizers has been studied. Transmittance was varied due to the magnetically induced reorientation of the nematic director from homeotropic to planar alignment. Two notable effects were observed for this scheme: the spectral shift of defect modes corresponding to the extraordinary light wave and its superposition with the ordinary one. As a result, the optical cell allows controlling the intensity of interfering defect modes by applied magnetic field. PMID:20173953

  16. Order by virtual crystal field fluctuations in pyrochlore XY antiferromagnets

    NASA Astrophysics Data System (ADS)

    Rau, Jeffrey G.; Petit, Sylvain; Gingras, Michel J. P.

    2016-05-01

    Conclusive evidence of order by disorder is scarce in real materials. Perhaps one of the strongest cases presented has been for the pyrochlore XY antiferromagnet Er2Ti2O7 , with the ground state selection proceeding by order by disorder induced through the effects of quantum fluctuations. This identification assumes the smallness of the effect of virtual crystal field fluctuations that could provide an alternative route to picking the ground state. Here we show that this order by virtual crystal field fluctuations is not only significant, but competitive with the effects of quantum fluctuations. Further, we argue that higher-multipolar interactions that are generically present in rare-earth magnets can dramatically enhance this effect. From a simplified bilinear-biquadratic model of these multipolar interactions, we show how the virtual crystal field fluctuations manifest in Er2Ti2O7 using a combination of strong-coupling perturbation theory and the random-phase approximation. We find that the experimentally observed ψ2 state is indeed selected and the experimentally measured excitation gap can be reproduced when the bilinear and biquadratic couplings are comparable while maintaining agreement with the entire experimental spin-wave excitation spectrum. Finally, we comment on possible tests of this scenario and discuss implications for other order-by-disorder candidates in rare-earth magnets.

  17. Crystal field and magnetic properties of ErH3

    NASA Technical Reports Server (NTRS)

    Flood, D. J.

    1977-01-01

    Magnetization and magnetic susceptibility measurements have been made in the temperature range 1.3 to 4.2 K on powdered samples of ErH3. The susceptibility exhibits Curie-Weiss behavior from 4.2 to 2 K, and intercepts the negative temperature axis at 1.05 + or - 0.05 K, indicating that the material is antiferromagnetic. The low field effective moment is 6.77 + or - 0.27 Bohr magnetons per ion. The magnetization exhibits a temperature independent contribution, the slope of which is (5 + or - 1.2) times 10 to the minus 6 Weber m/kg Tesla. The saturation moment is 3.84 + or - 0.15 Bohr magnetons per ion. The results can be qualitatively explained by the effects of crystal fields on the magnetic ions. No definitive assignment of a crystal field ground state can be given, nor can a clear choice between cubically or hexagonally symmetric crystal fields be made. For hexagonal symmetry, the first excited state is estimated to be 86 to 100 K above the ground state. For cubic symmetry, the splitting is of the order of 160 to 180 K.

  18. Effects of magnetic field and twin domains on magnetostructural phase mixture in Mn3O4 : Raman scattering studies of untwinned crystals

    NASA Astrophysics Data System (ADS)

    Byrum, T.; Gleason, S. L.; Thaler, A.; MacDougall, G. J.; Cooper, S. L.

    2016-05-01

    The ferrimagnetic spinel Mn3O4 exhibits large and anisotropic changes in electronic and structural properties in response to an applied magnetic field. These changes are thought to result from the field-dependent tuning—via strong spin-lattice coupling—between two nearly degenerate magnetostructural phases. Recent variable-magnetic-field studies of Mn3O4 have been performed on melt-grown crystals, which can exhibit twin domains due to a Jahn-Teller structural transition below the melting temperature. Because of the near degeneracy of the magnetostructural phases, however, strain associated with the twin domains likely affects the magnetic responses of Mn3O4 . In this report, we present a variable-magnetic-field Raman scattering study of untwinned Mn3O4 crystals grown out of a flux below the Jahn-Teller structural transition. We measure distinct q =0 magnetic and vibrational excitation spectra for each isolated magnetostructural phase of untwinned Mn3O4 crystals and determine the symmetries of the observed excitations. We determine how the magnetostructural phase mixture changes in response to magnetic fields applied in the magnetic easy plane. Last, by comparing results on flux- and melt-grown Mn3O4 crystals, we show that the intrinsic mixture of the two magnetostructural phases is indeed strongly influenced by the presence of twin domains.

  19. Paramagnetic Meissner effect at high fields in YCaBaCuO single crystal and melt-textured YBaCuO

    NASA Astrophysics Data System (ADS)

    Dias, F. T.; Vieira, V. N.; de Almeida, M. L.; Falck, A. L.; Pureur, P.; Pimentel, J. L.; Obradors, X.

    2010-12-01

    We report on systematic field-cooled magnetization experiments in an Y0.98Ca0.02Ba2Cu3O7-δ single crystal and melt-textured YBa2Cu3O7-δ samples. Magnetic fields up to 50 kOe were applied and a paramagnetic response related to the superconducting state was observed. We discuss our results in terms of the flux compression scenario into the sample.

  20. Magnetic Field Measurements Based on Terfenol Coated Photonic Crystal Fibers

    PubMed Central

    Quintero, Sully M. M.; Martelli, Cicero; Braga, Arthur M. B.; Valente, Luiz C. G.; Kato, Carla C.

    2011-01-01

    A magnetic field sensor based on the integration of a high birefringence photonic crystal fiber and a composite material made of Terfenol particles and an epoxy resin is proposed. An in-fiber modal interferometer is assembled by evenly exciting both eigenemodes of the HiBi fiber. Changes in the cavity length as well as the effective refractive index are induced by exposing the sensor head to magnetic fields. The magnetic field sensor has a sensitivity of 0.006 (nm/mT) over a range from 0 to 300 mT with a resolution about ±1 mT. A fiber Bragg grating magnetic field sensor is also fabricated and employed to characterize the response of Terfenol composite to the magnetic field. PMID:22247655

  1. The effect of an electric field on the morphological stability of the crystal-melt interface of a binary alloy

    NASA Technical Reports Server (NTRS)

    Wheeler, A. A.; Coriell, S. R.; Mcfadden, G. B.; Hurle, D. T. J.

    1988-01-01

    A fully time-dependent linear stability analysis of the morphological stability of a planar interface during directional solidification of a binary alloy at constant velocity in the presence of an electric field, is performed. The electromigration of solute and the differing electrical conductivities of solid and liquid for a model in which the temperature gradient is constant are taken into account. The present results are compared with the constitutional supercooling criterion, and it is shown there may be substantial differences. A modified constitutional supercooling criterion which is valid over a large range of conditions is derived. It is also found under certain conditions that the onset of instability may be time dependent.

  2. Using Magnetic Fields to Control Convection during Protein Crystallization: Analysis and Validation Studies

    NASA Technical Reports Server (NTRS)

    Ramachandran, N.; Leslie, F. W.

    2004-01-01

    The effect of convection during the crystallization of proteins is not very well understood. In a gravitational field, convection is caused by crystal sedimentation and by solutal buoyancy induced flow and these can lead to crystal imperfections. While crystallization in microgravity can approach diffusion limited growth conditions (no convection), terrestrially strong magnetic fields can be used to control fluid flow and sedimentation effects. In this work, we develop the analysis for magnetic flow control and test the predictions using analog experiments. Specifically, experiments on solutal convection in a paramagnetic fluid were conducted in a strong magnetic field gradient using a dilute solution of Manganese Chloride. The observed flows indicate that the magnetic field can completely counter the settling effects of gravity locally and are consistent with the theoretical predictions presented. This phenomenon suggests that magnetic fields may be useful in mimicking the microgravity environment of space for some crystal growth ana biological applications where fluid convection is undesirable.

  3. Influence of magnetic field on the morphology of the andrographolide crystal from supercritical carbon dioxide extraction crystallization

    NASA Astrophysics Data System (ADS)

    Chen, Kexun; Zhang, Xingyuan; Pan, Jian; Zhang, Wencheng; Yong, Ji; Yin, Wenhong

    2003-10-01

    In this paper, a supercritical fluid extraction-crystallization of andrographolide, a kind of Chinese traditional medicine, was investigated. We have studied the extraction-crystallization process with or without magnet in the extractor, respectively. It was found that the presence of magnetic field is an important factor influencing the quality of the products. SEM images showed that the crystal was slice-like in shape, and many slices reunited together in the absence of magnet. Further research showed that pressure had a certain effect on the morphology of the crystal.

  4. Impact of additional Pt and NiSi crystal orientation on channel stress induced by Ni silicide film in metal-oxide-semiconductor field-effect transistors

    NASA Astrophysics Data System (ADS)

    Mizuo, Mariko; Yamaguchi, Tadashi; Kudo, Shuichi; Hirose, Yukinori; Kimura, Hiroshi; Tsuchimoto, Jun-ichi; Hattori, Nobuyoshi

    2014-01-01

    The impact of additional Pt and Ni monosilicide (NiSi) crystal orientation on channel stress from Ni silicide in metal-oxide-semiconductor field-effect transistors (MOSFETs) has been demonstrated. The channel stress generation mechanism can be explained by the NiSi crystal orientation. In pure Ni silicide films, the channel stress in the p-type substrate is much larger than that in the n-type one, since the NiSi a-axis parallel to the channel direction is strongly aligned on the p-type substrate compared with on the n-type one. On the other hand, in NiPt silicide films, the difference in the channel stress between the p- and n-type substrates is small, because the NiSi crystal orientation on the p-type substrate is similar to that on the n-type one. These results can be explained by the Pt segregation at the interface between the NiSi film and the Si surface. Segregated Pt atoms cause the NiSi b-axis to align normal to the Si(001) surface in the nucleation step owing to the expansion of the NiSi lattice spacing at the NiSi/Si interface. Furthermore, the Pt segregation mechanism is considered to be caused by the grain boundary diffusion in the Ni2Si film during NiSi formation. We confirmed that the grains of Ni2Si on the p-type substrate are smaller than those on the n-type one. The Ni2Si film on the p-type substrate has more grain boundary diffusion paths than that on the n-type one. Therefore, the amount of Pt segregation at the NiSi/Si interface on the p-type substrate is larger than that on the n-type one. Consequently, the number of NiSi grains with the b-axis aligned normal to the Si(001) in the p-type substrate is larger than that in the n-type one. As a result, the channel stress induced by NiPt silicide in PMOS is larger than that in NMOS. According to this mechanism, controlling the Pt concentration at the NiSi/Si interface is one of the key factors for channel stress engineering.

  5. Semiconductor Crystal Growth in Static and Rotating Magnetic fields

    NASA Technical Reports Server (NTRS)

    Volz, Martin

    2004-01-01

    Magnetic fields have been applied during the growth of bulk semiconductor crystals to control the convective flow behavior of the melt. A static magnetic field established Lorentz forces which tend to reduce the convective intensity in the melt. At sufficiently high magnetic field strengths, a boundary layer is established ahead of the solid-liquid interface where mass transport is dominated by diffusion. This can have a significant effect on segregation behavior and can eliminate striations in grown crystals resulting from convective instabilities. Experiments on dilute (Ge:Ga) and solid solution (Ge-Si) semiconductor systems show a transition from a completely mixed convective state to a diffusion-controlled state between 0 and 5 Tesla. In HgCdTe, radial segregation approached the diffusion limited regime and the curvature of the solid-liquid interface was reduced by a factor of 3 during growth in magnetic fields in excess of 0.5 Tesla. Convection can also be controlled during growth at reduced gravitational levels. However, the direction of the residual steady-state acceleration vector can compromise this effect if it cannot be controlled. A magnetic field in reduced gravity can suppress disturbances caused by residual transverse accelerations and by random non-steady accelerations. Indeed, a joint program between NASA and the NHMFL resulted in the construction of a prototype spaceflight magnet for crystal growth applications. An alternative to the suppression of convection by static magnetic fields and reduced gravity is the imposition of controlled steady flow generated by rotating magnetic fields (RMF)'s. The potential benefits of an RMF include homogenization of the melt temperature and concentration distribution, and control of the solid-liquid interface shape. Adjusting the strength and frequency of the applied magnetic field allows tailoring of the resultant flow field. A limitation of RMF's is that they introduce deleterious instabilities above a

  6. Investigation of electric field effect on the third order nonlinear optical properties of Fe3O4 nanoparticles-doped nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Dehghani, Z.; Saievar Iranizad, E.; Nadafan, M.

    2015-01-01

    Third order nonlinearity of Fe3O4 nanoparticles (NPs) doped in nematic liquid crystals (NLCs) was evaluated due to laser induced self-phase modulation. The influence of electric field on the nonlinear optical responses of the NLCs doped with Fe3O4 NPs was considered in different voltages. The measurements were performed for two commonly initial alignments (homogeneous and homeotropic) with different small compositional percentages of magnetic NPs. The experimental results show that the homogenous- aligned cell was considerably affected on the applied electric field while the nonlinearity of homeotropic-aligned NLCs with the Fe3O4 NPs did not approximately change in the presence of electric field.

  7. Electric heating effects in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Yin, Y.; Shiyanovskii, S. V.; Lavrentovich, O. D.

    2006-07-01

    Electric heating effects in the nematic liquid crystal change the liquid crystal physical properties and dynamics. We propose a model to quantitatively describe the heating effects caused by dielectric dispersion and ionic conductivity in the nematic liquid crystals upon the application of an ac electric field. The temperature increase of the liquid crystal cell is related to the properties of the liquid crystal such as the imaginary part of the dielectric permittivity, thermal properties of the bounding plates, and the surrounding medium as well as frequency and amplitude of the electric field. To study the temperature dynamics experimentally, we use a small thermocouple inserted directly into the nematic bulk; we assure that the thermocouple does not alter the thermal behavior of the system by comparing the results to those obtained by a noncontact birefringent probing technique recently proposed by Wen and Wu [Appl. Phys. Lett. 86, 231104 (2005)]. We determine how the temperature dynamics and the stationary value of the temperature increase depend on the parameters of the materials and the applied field. We used different surrounding media, from extremely good heat conductors such as aluminum cooling device to extremely poor conductor, Styrofoam; these two provide two limiting cases as compared to typical conditions of nematic cell exploitation in a laboratory or in commercial devices. The experiments confirm the theoretical predictions, namely, that the temperature rise is controlled not only by the heat transfer coefficient of the surrounding medium (as in the previous model) but also by the thickness and the thermal conductivity coefficient of the bounding plates enclosing the nematic layer. The temperature increase strongly depends on the director orientation and can change nonmonotonously with the frequency of the applied field.

  8. Novel vertical hetero- and homo-junction tunnel field-effect transistors based on multi-layer 2D crystals

    NASA Astrophysics Data System (ADS)

    Lu, Shang-Chun; Mohamed, Mohamed; Zhu, Wenjuan

    2016-03-01

    Vertical hetero- and homo-junction tunnel FET (TFET) based on multi-layer black phosphorus (BP) and transition metal dichalcogenides are proposed and studied by numerical simulations employing the semi-classical density gradient quantum correction model. It is found that the vertical TFET based on BP can achieve high on-current (>200 μA μm-1) and steep subthreshold swing (average value = 24.6 mV/dec) simultaneously, due to its high mobility, direct narrow bandgap, and low dielectric constant. We also found that the on-current in vertical TFETs based on MoS2/MoSe2 hetero-junction is two orders of magnitudes higher than the one in MoS2 homo-junction TFET, due to the reduced effective bandgap in heterostructure with staggered band alignment. In addition, we present various design considerations and recommendations as well as provide a qualitative comparison with published data.

  9. Analysis of NAD(P)+/NAD(P)H cofactors by imprinted polymer membranes associated with ion-sensitive field-effect transistor devices and Au-quartz crystals.

    PubMed

    Pogorelova, Svetlana P; Zayats, Maya; Bourenko, Tatyana; Kharitonov, Andrei B; Lioubashevski, Oleg; Katz, Eugenii; Willner, Itamar

    2003-02-01

    Specific recognition sites for the NAD(P)+ and NAD(P)H cofactors are imprinted in a cross-linked acrylamide-acrylamidophenylboronic acid copolymer membrane. The imprinted membranes, associated with pH-sensitive field-effect transistors (ISFETs) or Au-quartz piezoelectric crystals, enable the potentiometric or microgravimetric analysis of the oxidized NAD(P)+ cofactors and the reduced NAD(P)H cofactors, respectively. The NAD+- and NADP+-imprinted membranes associated with the ISFET allow the analysis of NAD+ and NADP+ with sensitivities that correspond to 15.0 and 18.0 mVdecade(-1) and detection limits of 4 x 10(-7) and 2 x 10(-7) M, respectively. The NADH- and NADPH-imprinted membranes associated with the ISFET device enable the analysis of NADH and NADPH with sensitivities that correspond to 24.2 and 21.8 mV x decade(-1) and lower detection limits that are 1 x 10(-7) and 2 x 10(-7) M, respectively. The ISFET devices functionalized with the NADH and NADPH membranes are employed in the analysis of the biocatalyzed oxidation of lactic acid and ethanol in the presence of lactate dehydrogenase and alcohol dehydrogenase, respectively. PMID:12585477

  10. Subsurface Stress Fields In Single Crystal (Anisotropic) Contacts

    NASA Technical Reports Server (NTRS)

    Arakere, Nagaraj K.; Knudsen, Erik C.; Duke, Greg; Battista, Gilda; Swanson, Greg

    2004-01-01

    Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and alternating stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent HCF failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and noncrystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. This paper presents analytical and numerical techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts. The subsurface stress results are required for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades. An analytical procedure is , presented, for evaluating the subsurface stresses in the elastic half-space, using a complex potential method outlined by Lekhnitskii. Numerical results are presented for cylindrical and spherical anisotropic contacts, using finite element analysis. Effects of crystal orientation on stress response and fatigue life are examined.

  11. Size effects in spin-crossover nanoparticles in framework of 2D and 3D Ising-like breathing crystal field model

    NASA Astrophysics Data System (ADS)

    Gudyma, Iu.; Maksymov, A.; Spinu, L.

    2015-10-01

    The spin-crossover nanoparticles of different sizes and stochastic perturbations in external field taking into account the influence of the dimensionality of the lattice was studied. The analytical tools used for the investigation of spin-crossover system are based on an Ising-like model described using of the breathing crystal field concept. The changes of transition temperatures characterizing the systems' bistable properties for 2D and 3D lattices, and their dependence on its size and fluctuations strength were obtained. The state diagrams with hysteretic and non-hysteretic behavior regions have also been determined.

  12. Magnetic rotations of uric acid crystals and uratic crystals by static magnetic fields of up to 500 mT.

    PubMed

    Takeuchi, Yuka; Mizukawa, Yuri; Iwasaka, Masakazu

    2013-01-01

    In recent years, the disease concerning ureteral calculus is increasing possibly due to the changing lifestyles. For example, it is well known that the urinary calculi have a large impact to gout. As eating habitual diseases, gout and the hyper-uricemia are related to the formation of urinary calculus. In the previous studies, therapeutic agents were developed to enhance the uric acid excretion. From the viewpoint of side effects induction by the chemical agents, we are motivated to explore an alternative method to control the formation of ureteral crystals stimulator by physical stimulations. Therefore in the present study, we focused on the behaviors of uric acid crystals under magnetic fields of several hundreds of mT (Tesla). The uric acid crystals were re-crystallized from a suspension of uric acid powder, and the micro-crystals were prepared to be floating in the solution. We generated horizontal magnetic fields of maximum 500 mT by an electromagnet which contained a CCD microscope. A permanent magnet with magnetic fields of 200∼400 mT was also utilized. During the magnetic fields were applied to the uric acid crystals, we observed that the uric acid crystals were oriented by the magnetic fields down to 200 mT at the room temperature. It was speculated that the dimagnetic anisotropy in the uric acid crystals exhibited the rotational responses. The results indicate the possible remote control of the uric acid crystals in living body by the magnetic fields of 200 mT to 500 mT. PMID:24110424

  13. Field expulsion and reconfiguration in polaritonic photonic crystals.

    PubMed

    Huang, Kerwyn Casey; Bienstman, Peter; Joannopoulos, John D; Nelson, Keith A; Fan, Shanhui

    2003-05-16

    We uncover a rich set of optical phenomena stemming from the incorporation of polar materials exhibiting transverse phonon polariton excitations into a photonic crystal structure. We identify in the frequency spectrum two regimes in which the dielectric response of the polaritonic medium can induce extreme localization of the electromagnetic energy. Our analysis of the effect of polarization and the interaction between the polariton and photonic band gaps on the Bloch states leads to a pair of mechanisms for sensitive frequency-controlled relocation and/or reconfiguration of the fields. PMID:12785962

  14. Subsurface Stress Fields in FCC Single Crystal Anisotropic Contacts

    NASA Technical Reports Server (NTRS)

    Arakere, Nagaraj K.; Knudsen, Erik; Swanson, Gregory R.; Duke, Gregory; Ham-Battista, Gilda

    2004-01-01

    Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and alternating stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent high cycle fatigue (HCF) failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and non-crystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. This paper presents analytical and numerical techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts. The subsurface stress results are required for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades. An analytical procedure is presented for evaluating the subsurface stresses in the elastic half-space, based on the adaptation of a stress function method outlined by Lekhnitskii. Numerical results are presented for cylindrical and spherical anisotropic contacts, using finite element analysis (FEA). Effects of crystal orientation on stress response and fatigue life are examined. Obtaining accurate subsurface stress results for anisotropic single crystal contact problems require extremely refined three-dimensional (3-D) finite element grids, especially in the edge of contact region. Obtaining resolved shear stresses (RSS) on the principal slip planes also involves

  15. Enhancement of crystal homogeneity of protein crystals under application of an external alternating current electric field

    SciTech Connect

    Koizumi, H.; Uda, S.; Fujiwara, K.; Nozawa, J.; Tachibana, M.; Kojima, K.

    2014-10-06

    X-ray diffraction rocking-curve measurements were performed on tetragonal hen egg white (HEW) lysozyme crystals grown with and without the application of an external alternating current (AC) electric field. The crystal quality was assessed by the full width at half maximum (FWHM) value for each rocking curve. For two-dimensional maps of the FWHMs measured on the 440 and the 12 12 0 reflection, the crystal homogeneity was improved under application of an external electric field at 1 MHz, compared with that without. In particular, the significant improvement of the crystal homogeneity was observed for the 12 12 0 reflection.

  16. Hidden local symmetry of Eu{sup 3+} in xenotime-like crystals revealed by high magnetic fields

    SciTech Connect

    Han, Yibo; Ma, Zongwei; Zhang, Junpei; Wang, Junfeng; Du, Guihuan; Xia, Zhengcai; Han, Junbo Li, Liang; Yu, Xuefeng

    2015-02-07

    The excellent optical properties of europium-doped crystals in visible and near infrared wavelength regions enable them to have broad applications in optoelectronics, laser crystals and sensing devices. The local site crystal fields can affect the intensities and peak positions of the photo-emission lines strongly, but they are usually difficult to be clarified due to magnetically degenerate 4f electronic levels coupling with the crystal fields. Here, we provide an effective way to explore the hidden local symmetry of the Eu{sup 3+} sites in different hosts by taking photoluminescence measurements under pulsed high magnetic fields up to 46 T. The zero-field photoluminescence peaks split further at high magnetic fields when the Zeeman splitting energy is comparable to or larger than that of the crystal field induced zero-field splitting. In particular, a magnetic field induced crossover of the local crystal fields has been observed in the GdVO{sub 4}:Eu{sup 3+} crystal, which resulted from the alignment of Gd{sup 3+} magnetic moment in high magnetic fields; and a hexagonally symmetric local crystal fields was observed in the YPO{sub 4} nanocrystals at the Eu{sup 3+} sites characterized by the special axial and rhombic crystal field terms. These distinct Zeeman splitting behaviors uncover the crystal fields-related local symmetry of luminescent Eu{sup 3+} centers in different hosts or magnetic environments, which are significant for their applications in optics and optoelectronics.

  17. An efficient algorithm for solving the phase field crystal model

    SciTech Connect

    Cheng Mowei Warren, James A.

    2008-06-01

    We present and discuss the development of an unconditionally stable algorithm used to solve the evolution equations of the phase field crystal (PFC) model. This algorithm allows for an arbitrarily large algorithmic time step. As the basis for our analysis of the accuracy of this algorithm, we determine an effective time step in Fourier space. We then compare our calculations with a set of representative numerical results, and demonstrate that this algorithm is an effective approach for the study of the PFC models, yielding a time step effectively 180 times larger than the Euler algorithm for a representative set of material parameters. As the PFC model is just a simple example of a wide class of density functional theories, we expect this method will have wide applicability to modeling systems of considerable interest to the materials modeling communities.

  18. Pendellösung effect in photonic crystals

    NASA Astrophysics Data System (ADS)

    Savo, S.; di Gennaro, E.; Miletto, C.; Andreone, A.; Dardano, P.; Moretti, L.; Mocella, V.

    2008-06-01

    At the exit surface of a photonic crystal, the intensity of the diffracted wave can be periodically modulated, showing a maximum in the "positive" (forward diffracted) or in the "negative" (diffracted) direction, depending on the slab thickness. This thickness dependence is a direct result of the so-called Pendellosung phenomenon, consisting of the periodic exchange inside the crystal of the energy between direct and diffracted beams. We report the experimental observation of this effect in the microwave region at about 14 GHz by irradiating 2D photonic crystal slabs of different thickness and detecting the intensity distribution of the electromagnetic field at the exit surface and inside the crystal itself.

  19. Effects of impurities on crystal growth in fructose crystallization

    NASA Astrophysics Data System (ADS)

    Chu, Y. D.; Shiau, L. D.; Berglund, K. A.

    1989-10-01

    The influence of impurities on the crystallization of anhydrous fructose from aqueous solution was studied. The growth kinetics of fructose crystals in the fructose-water-glucose and fructose-water-difructose dianhydrides systems were investigated using photomicroscopic contact nucleation techniques. Glucose is the major impurity likely to be present in fructose syrup formed during corn wet milling, while several difructose dianhydrides are formed in situ under crystallization conditions and have been proposed as a cause in the decrease of overall yields. Both sets of impurities were found to cause inhibition of crystal growth, but the mechanisms responsible in each case are different. It was found that the presence of glucose increases the solubility of fructose in water and thus lowers the supersaturation of the solution. This is probably the main effect responsible for the decrease of crystal growth. Since the molecular structures of difructose dianhydrides are similar to that of fructose, they are probably "tailor-made" impurities. The decrease of crystal growth is probably caused by the incorporation of these impurities into or adsorption to the crystal surface which would accept fructose molecules in the orientation that existed in the difructose dianhydride.

  20. Energy levels fitting and crystal-field calculations of Nd3+ doped in GYSGG crystal

    NASA Astrophysics Data System (ADS)

    Gao, Jinyun; Zhang, Qingli; Sun, Dunlu; Luo, Jianqiao; Liu, Wenpeng; Yin, Shaotang

    2012-10-01

    The single crystal Nd3+-doped in GdY2Sc2Ga3O12 (Nd3+:GYSGG) was grown by Czochralski method successfully, and its absorption spectra was analyzed in a wider spectral wavelength range at 7.6 K and 300 K, respectively. The free-ions and crystal-field parameters were fitted to the experimental energy levels at 7.6 K and 300 K with the root mean square deviation of 11.25 and 12.48 cm-1, respectively. According to the crystal-field calculations, 116 levels of Nd3+ at 7.6 K and 114 levels of Nd3+ at 300 K were assigned. The fitting results of free-ions and crystal-field parameters were compared with those already reported of Nd3+:GSGG and Nd3+:YSAG. The results indicated that the free-ions parameters are similar to those of the Nd3+ in GYSGG, GSGG and YSAG crystals, and the crystal-field interaction of GSGG and YSAG is stronger than that of GYSGG, which results in the dual-wavelength properties of Nd3+:GYSGG crystal.

  1. Crystal field spectra of lunar pyroxenes.

    NASA Technical Reports Server (NTRS)

    Burns, R. G.; Abu-Eid, R. M.; Huggins, F. E.

    1972-01-01

    Absorption spectra in the visible and near infrared regions have been obtained for pyroxene single crystals in rocks from the Apollo 11, 12, 14, and 15 missions. The polarized spectra are compared with those obtained from terrestrial calcic clinopyroxenes, subcalcic augites, pigeonites, and orthopyroxenes. The lunar pyroxenes contain several broad, intense absorption bands in the near infrared, the positions of which are related to bulk composition, Fe(2+) site occupancy and structure type of the pyroxene. The visible spectra contain several sharp, weak peaks mainly due to spin-forbidden transitions in Fe(2+). Additional weak bands in this region in Apollo 11 pyroxenes are attributed to Ti(3+) ions. Spectral features from Fe(3+), Mn(2+), Cr(3+), and Cr(2+) were not observed.

  2. Heat transport in polymer-dispersed liquid crystals under electric field

    NASA Astrophysics Data System (ADS)

    Hadj Sahraoui, Abdelhak; Delenclos, Sylvain; Longuemart, Stéphane; Dadarlat, Dorin

    2011-08-01

    The concepts of effective thermal conductivity and interfacial thermal contact resistance in composite media are applied to study heat transport in polymer-dispersed liquid crystals (PDLC). In these systems, the thermal properties of liquid crystal inclusions are changed by an imposed electric field. The photopyroelectric (PPE) technique with a cell allowing the application of an electric field to the sample is used to measure the thermal parameters. A model based on effective medium approximation is used to assess the impact of interfaces on the flow of heat through the determination of the Kapitza radius. It was found that the effect of interfaces becomes dominant compared to the volume conduction of the droplet when the liquid crystal (LC) droplet radius becomes smaller than 1 micron. The comparison of the thermal behavior of LC in the droplets with that of bulk liquid crystal allowed to evaluate the effect of confinement on the LC nematic phase.

  3. Modeling nuclear volume isotope effects in crystals

    NASA Astrophysics Data System (ADS)

    Schauble, Edwin A.

    2013-10-01

    Mass-independent isotope fractionations driven by differences in volumes and shapes of nuclei (the field shift effect) are known in several elements and are likely to be found in more. All-electron relativistic electronic structure calculations can predict this effect but at present are computationally intensive and limited to modeling small gas phase molecules and clusters. Density functional theory, using the projector augmented wave method (DFT-PAW), has advantages in greater speed and compatibility with a three-dimensional periodic boundary condition while preserving information about the effects of chemistry on electron densities within nuclei. These electron density variations determine the volume component of the field shift effect. In this study, DFT-PAW calculations are calibrated against all-electron, relativistic Dirac-Hartree-Fock, and coupled-cluster with single, double (triple) excitation methods for estimating nuclear volume isotope effects. DFT-PAW calculations accurately reproduce changes in electron densities within nuclei in typical molecules, when PAW datasets constructed with finite nuclei are used. Nuclear volume contributions to vapor-crystal isotope fractionation are calculated for elemental cadmium and mercury, showing good agreement with experiments. The nuclear-volume component of mercury and cadmium isotope fractionations between atomic vapor and montroydite (HgO), cinnabar (HgS), calomel (Hg2Cl2), monteponite (CdO), and the CdS polymorphs hawleyite and greenockite are calculated, indicating preferential incorporation of neutron-rich isotopes in more oxidized, ionically bonded phases. Finally, field shift energies are related to Mössbauer isomer shifts, and equilibrium mass-independent fractionations for several tin-bearing crystals are calculated from 119Sn spectra. Isomer shift data should simplify calculations of mass-independent isotope fractionations in other elements with Mössbauer isotopes, such as platinum and uranium.

  4. Modeling nuclear volume isotope effects in crystals

    PubMed Central

    Schauble, Edwin A.

    2013-01-01

    Mass-independent isotope fractionations driven by differences in volumes and shapes of nuclei (the field shift effect) are known in several elements and are likely to be found in more. All-electron relativistic electronic structure calculations can predict this effect but at present are computationally intensive and limited to modeling small gas phase molecules and clusters. Density functional theory, using the projector augmented wave method (DFT-PAW), has advantages in greater speed and compatibility with a three-dimensional periodic boundary condition while preserving information about the effects of chemistry on electron densities within nuclei. These electron density variations determine the volume component of the field shift effect. In this study, DFT-PAW calculations are calibrated against all-electron, relativistic Dirac–Hartree–Fock, and coupled-cluster with single, double (triple) excitation methods for estimating nuclear volume isotope effects. DFT-PAW calculations accurately reproduce changes in electron densities within nuclei in typical molecules, when PAW datasets constructed with finite nuclei are used. Nuclear volume contributions to vapor–crystal isotope fractionation are calculated for elemental cadmium and mercury, showing good agreement with experiments. The nuclear-volume component of mercury and cadmium isotope fractionations between atomic vapor and montroydite (HgO), cinnabar (HgS), calomel (Hg2Cl2), monteponite (CdO), and the CdS polymorphs hawleyite and greenockite are calculated, indicating preferential incorporation of neutron-rich isotopes in more oxidized, ionically bonded phases. Finally, field shift energies are related to Mössbauer isomer shifts, and equilibrium mass-independent fractionations for several tin-bearing crystals are calculated from 119Sn spectra. Isomer shift data should simplify calculations of mass-independent isotope fractionations in other elements with Mössbauer isotopes, such as platinum and uranium

  5. Modeling nuclear volume isotope effects in crystals.

    PubMed

    Schauble, Edwin A

    2013-10-29

    Mass-independent isotope fractionations driven by differences in volumes and shapes of nuclei (the field shift effect) are known in several elements and are likely to be found in more. All-electron relativistic electronic structure calculations can predict this effect but at present are computationally intensive and limited to modeling small gas phase molecules and clusters. Density functional theory, using the projector augmented wave method (DFT-PAW), has advantages in greater speed and compatibility with a three-dimensional periodic boundary condition while preserving information about the effects of chemistry on electron densities within nuclei. These electron density variations determine the volume component of the field shift effect. In this study, DFT-PAW calculations are calibrated against all-electron, relativistic Dirac-Hartree-Fock, and coupled-cluster with single, double (triple) excitation methods for estimating nuclear volume isotope effects. DFT-PAW calculations accurately reproduce changes in electron densities within nuclei in typical molecules, when PAW datasets constructed with finite nuclei are used. Nuclear volume contributions to vapor-crystal isotope fractionation are calculated for elemental cadmium and mercury, showing good agreement with experiments. The nuclear-volume component of mercury and cadmium isotope fractionations between atomic vapor and montroydite (HgO), cinnabar (HgS), calomel (Hg2Cl2), monteponite (CdO), and the CdS polymorphs hawleyite and greenockite are calculated, indicating preferential incorporation of neutron-rich isotopes in more oxidized, ionically bonded phases. Finally, field shift energies are related to Mössbauer isomer shifts, and equilibrium mass-independent fractionations for several tin-bearing crystals are calculated from (119)Sn spectra. Isomer shift data should simplify calculations of mass-independent isotope fractionations in other elements with Mössbauer isotopes, such as platinum and uranium. PMID

  6. The flow structure in the near field of jets and its effect on cavitation inception, and, Implementation of ferroelectric liquid crystal and birefringent crystal for image shifting in particle image velocimetry

    NASA Astrophysics Data System (ADS)

    Gopalan, Shridhar

    1999-10-01

    Cavitation experiments performed in the near field of a 50-mm diameter (D) jet at ReD = 5 × 105, showed inception in the form of inclined ``cylindrical'' bubbles at axial distances (x/D) less than 0.55, with indices of 2.5. On tripping the boundary layer, cavitation inception occurred at x/D ~ 2, as distorted ``spherical'' bubbles with inception indices of 1.7. To investigate these substantial differences, the near field of the jet was measured using Particle Image Velocimetry (PIV). Data on the primary flow, the strength distribution of the ``streamwise''vortices and the velocity profiles within the initial boundary layers were obtained. The untripped case showed a direct transition to three-dimensional flow in the near field (x/D < 0.7) even before rolling up to distinct vortex rings. Strong ``streamwise'' vortices with strengths up to 25% of the jet velocity times the characteristic wavelength were seen. Cavitation inception occurred in the core of these vortices. In contrast, in the tripped jet the vortex sheet rolled up to the familiar Kelvin- Helmholtz vortex rings with weak secondary vortices. Using the measured nuclei distribution, strengths and straining of the ``streamwise'' structures, the rates of cavitation events were estimated. The estimated results match very well with the measured cavitation rates. Also, the Reynolds stresses in the near field of the jet show similar trends and magnitudes to those of Browand & Latigo (1979) and Bell & Mehta (1990) for a plane shear layer. In the second part of this essay we discuss the implementation of electro-optical image shifting to resolve directional ambiguity in PIV measurements. The technique uses a ferroelectric liquid crystal (FLC) as an electro-optic half wave plate and a birefringent crystal (calcite) as the shifter. The system can be used with non-polarized light sources and fluorescent particles. The minimum shifting time is approximately 100μs. This compact electrooptical device usually is

  7. Modeling nuclear field shift isotope fractionation in crystals

    NASA Astrophysics Data System (ADS)

    Schauble, E. A.

    2013-12-01

    In this study nuclear field shift fractionations in solids (and chemically similar liquids) are estimated using calibrated density functional theory calculations. The nuclear field shift effect is a potential driver of mass independent isotope fractionation(1,2), especially for elements with high atomic number such as Hg, Tl and U. This effect is caused by the different shapes and volumes of isotopic nuclei, and their interactions with electronic structures and energies. Nuclear field shift isotope fractionations can be estimated with first principles methods, but the calculations are computationally difficult, limiting most theoretical studies so far to small gas-phase molecules and molecular clusters. Many natural materials of interest are more complex, and it is important to develop ways to estimate field shift effects that can be applied to minerals, solutions, in biomolecules, and at mineral-solution interfaces. Plane-wave density functional theory, in combination with the projector augmented wave method (DFT-PAW), is much more readily adapted to complex materials than the relativistic all-electron calculations that have been the focus of most previous studies. DFT-PAW is a particularly effective tool for studying crystals with periodic boundary conditions, and may also be incorporated into molecular dynamics simulations of solutions and other disordered phases. Initial calibrations of DFT-PAW calculations against high-level all-electron models of field shift fractionation suggest that there may be broad applicability of this method to a variety of elements and types of materials. In addition, the close relationship between the isomer shift of Mössbauer spectroscopy and the nuclear field shift isotope effect makes it possible, at least in principle, to estimate the volume component of field shift fractionations in some species that are too complex even for DFT-PAW models, so long as there is a Mössbauer isotope for the element of interest. Initial results

  8. Control of active liquid crystals with a magnetic field.

    PubMed

    Guillamat, Pau; Ignés-Mullol, Jordi; Sagués, Francesc

    2016-05-17

    Living cells sense the mechanical features of their environment and adapt to it by actively remodeling their peripheral network of filamentary proteins, known as cortical cytoskeleton. By mimicking this principle, we demonstrate an effective control strategy for a microtubule-based active nematic in contact with a hydrophobic thermotropic liquid crystal. By using well-established protocols for the orientation of liquid crystals with a uniform magnetic field, and through the mediation of anisotropic shear stresses, the active nematic reversibly self-assembles with aligned flows and textures that feature orientational order at the millimeter scale. The turbulent flow, characteristic of active nematics, is in this way regularized into a laminar flow with periodic velocity oscillations. Once patterned, the microtubule assembly reveals its intrinsic length and time scales, which we correlate with the activity of motor proteins, as predicted by existing theories of active nematics. The demonstrated commanding strategy should be compatible with other viable active biomaterials at interfaces, and we envision its use to probe the mechanics of the intracellular matrix. PMID:27140604

  9. Magnetic Field Applications in Semiconductor Crystal Growth and Metallurgy

    NASA Technical Reports Server (NTRS)

    Mazuruk, Konstantin; Ramachandran, Narayanan; Grugel, Richard; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    The Traveling Magnetic Field (TMF) technique, recently proposed to control meridional flow in electrically conducting melts, is reviewed. In particular, the natural convection damping capability of this technique has been numerically demonstrated with the implication of significantly improving crystal quality. Advantages of the traveling magnetic field, in comparison to the more mature rotating magnetic field method, are discussed. Finally, results of experiments with mixing metallic alloys in long ampoules using TMF is presented

  10. Scale effects in crystal plasticity

    NASA Astrophysics Data System (ADS)

    Padubidri Janardhanachar, Guruprasad

    The goal of this research work is to further the understanding of crystal plasticity, particularly at reduced structural and material length scales. Fundamental understanding of plasticity is central to various challenges facing design and manufacturing of materials for structural and electronic device applications. The development of microstructurally tailored advanced metallic materials with enhanced mechanical properties that can withstand extremes in stress, strain, and temperature, will aid in increasing the efficiency of power generating systems by allowing them to work at higher temperatures and pressures. High specific strength materials can lead to low fuel consumption in transport vehicles. Experiments have shown that enhanced mechanical properties can be obtained in materials by constraining their size, microstructure (e.g. grain size), or both for various applications. For the successful design of these materials, it is necessary to have a thorough understanding of the influence of different length scales and evolving microstructure on the overall behavior. In this study, distinction is made between the effect of structural and material length scale on the mechanical behavior of materials. A length scale associated with an underlying physical mechanism influencing the mechanical behavior can overlap with either structural length scales or material length scales. If it overlaps with structural length scales, then the material is said to be dimensionally constrained. On the other hand, if it overlaps with material length scales, for example grain size, then the material is said to be microstructurally constrained. The objectives of this research work are: (1) to investigate scale and size effects due to dimensional constraints; (2) to investigate size effects due to microstructural constraints; and (3) to develop a size dependent hardening model through coarse graining of dislocation dynamics. A discrete dislocation dynamics (DDD) framework where the

  11. Rashba coupling amplification by a staggered crystal field

    PubMed Central

    Santos-Cottin, David; Casula, Michele; Lantz, Gabriel; Klein, Yannick; Petaccia, Luca; Le Fèvre, Patrick; Bertran, François; Papalazarou, Evangelos; Marsi, Marino; Gauzzi, Andrea

    2016-01-01

    There has been increasing interest in materials where relativistic effects induce non-trivial electronic states with promise for spintronics applications. One example is the splitting of bands with opposite spin chirality produced by the Rashba spin-orbit coupling in asymmetric potentials. Sizable splittings have been hitherto obtained using either heavy elements, where this coupling is intrinsically strong, or large surface electric fields. Here by means of angular resolved photoemission spectroscopy and first-principles calculations, we give evidence of a large Rashba coupling of 0.25 eV Å, leading to a remarkable band splitting up to 0.15 eV with hidden spin-chiral polarization in centrosymmetric BaNiS2. This is explained by a huge staggered crystal field of 1.4 V Å−1, produced by a gliding plane symmetry, that breaks inversion symmetry at the Ni site. This unexpected result in the absence of heavy elements demonstrates an effective mechanism of Rashba coupling amplification that may foster spin-orbit band engineering. PMID:27089869

  12. Rashba coupling amplification by a staggered crystal field

    NASA Astrophysics Data System (ADS)

    Santos-Cottin, David; Casula, Michele; Lantz, Gabriel; Klein, Yannick; Petaccia, Luca; Le Fèvre, Patrick; Bertran, François; Papalazarou, Evangelos; Marsi, Marino; Gauzzi, Andrea

    2016-04-01

    There has been increasing interest in materials where relativistic effects induce non-trivial electronic states with promise for spintronics applications. One example is the splitting of bands with opposite spin chirality produced by the Rashba spin-orbit coupling in asymmetric potentials. Sizable splittings have been hitherto obtained using either heavy elements, where this coupling is intrinsically strong, or large surface electric fields. Here by means of angular resolved photoemission spectroscopy and first-principles calculations, we give evidence of a large Rashba coupling of 0.25 eV Å, leading to a remarkable band splitting up to 0.15 eV with hidden spin-chiral polarization in centrosymmetric BaNiS2. This is explained by a huge staggered crystal field of 1.4 V Å-1, produced by a gliding plane symmetry, that breaks inversion symmetry at the Ni site. This unexpected result in the absence of heavy elements demonstrates an effective mechanism of Rashba coupling amplification that may foster spin-orbit band engineering.

  13. Study of Fluid Flow Control in Protein Crystallization using Strong Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Ramachandran, Narayanan; Leslie, Fred; Ciszak, Ewa

    2002-01-01

    positioning the crystal growth cell so that the magnetic susceptibility force counteracts terrestrial gravity. The general objective is to test the hypothesis of convective control using a strong magnetic field and magnetic field gradient and to understand the nature of the various forces that come into play. Specifically we aim to delineate causative factors and to quantify them through experiments, analysis and numerical modeling. Once the basic understanding is obtained, the study will focus on testing the hypothesis on proteins of pyruvate dehydrogenase complex (PDC), proteins E1 and E3. Obtaining high crystal quality of these proteins is of great importance to structural biologists since their structures need to be determined. Specific goals for the investigation are: 1. To develop an understanding of convection control in diamagnetic fluids with concentration gradients through experimentation and numerical modeling. Specifically solutal buoyancy driven convection due to crystal growth will be considered. 2. To develop predictive measures for successful crystallization in a magnetic field using analyses and numerical modeling for use in future protein crystal growth experiments. This will establish criteria that can be used to estimate the efficacy of magnetic field flow damping on crystallization of candidate proteins. 3. To demonstrate the understanding of convection damping by high magnetic fields to a class of proteins that is of interest and whose structure is as yet not determined. 4. To compare quantitatively, the quality of the grown crystals with and without a magnetic field. X-ray diffraction techniques will be used for the comparative studies. In a preliminary set of experiments, we studied crystal dissolution effects in a 5 Tesla magnet available at NASA Marshall Space Flight Center (MSFC). Using a Schlieren setup, a 1mm crystal of Alum (Aluminum-Potassium Sulfate) was introduced in a 75% saturated solution and the resulting dissolution plume was observed

  14. Control over colloidal crystallization by shear and electric fields

    NASA Astrophysics Data System (ADS)

    Wu, Y. L.

    2007-05-01

    We used shear flow and an electric field to control colloidal crystallization. The structures were examined in situ with confocal microscopy. For experiments under shear, a new parallel plate shear cell was designed. It had a zero-velocity plane that was stationary with respect to the microscope. The plates were microscopy slides of a few square centimeters. They both had a maximum travel of 1 cm and for the systems that we study an oscillatory shear with such a large amplitude can be regarded as a continuous shear. The gap width was variable between 20- 200 m. The plates were parallel within 1-2 m. The flow profile of a dilute suspension was linear, but that of a crystallizing dispersion appeared to be non-linear. At the walls a sliding layer structure formed of which the local viscosity was 1.5 times smaller than that of the liquid-like structure in the middle of the gap. At low shear rates hexagonal layers of a crystal showed a zigzag motion. We also examined shear melting and crystallization. Shear melting appeared to be a local process in which the local order sometimes increased and sometimes decreased while the average order decreased. Shear induced crystallization occurred uniformly over the sample and the order increased monotonously. By spin coating colloidal crystalline films were fabricated that consisted of randomly stacked hexagonal layers. The structures could be made permanent by using a dispersing medium that could be polymerized. The interparticle spacing was not fixed, but probably depended subtly on the surface charge of the particles and the ionic strength of the medium. Different from crystals formed by sedimentation, spin coated crystals were crystalline to the top. This is one of the indications that crystal formation started at the air interface with a 2D layer that grew into a 3D multilayer structure while it was sedimenting. From these spin coated crystals freestanding colloidal crystalline films could be made. Without crack

  15. Bridgman Growth of Germanium Crystals in a Rotating Magnetic Field

    NASA Technical Reports Server (NTRS)

    Volz, M. P.; Schweizer, M.; Cobb, S. D.; Walker, J. S.; Szofran, F. R.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    A series of (100)-oriented gallium-doped germanium crystals have been grown by the Bridgman method and under the influence of a rotating magnetic field (RMF). The RMF has a marked affect on the interface shape, changing it from concave to nearly flat. The onset of time-dependent flow instabilities occurs when the critical magnetic Taylor number is exceeded, and this can be observed by noting the appearance of striations in the grown crystals. The critical magnetic Taylor number is a sensitive function of the aspect ratio and, as the crystal grows under a constant applied magnetic field, the induced striations change from nonperiodic to periodic, undergo a period-doubling transition, and then cease to exist. Also, by pulsing the RMF on and off, it is shown that intentional interface demarcations can be introduced.

  16. Effects of trace elements on the crystal field parameters of Nd ions at the surface of Nd{sub 2}Fe{sub 14}B grains

    SciTech Connect

    Toga, Yuta; Suzuki, Tsuneaki; Sakuma, Akimasa

    2015-06-14

    Using first-principles calculations, we investigate the positional dependence of trace elements such as O and Cu on the crystal field parameter A{sub 2}{sup 0}, proportional to the magnetic anisotropy constant K{sub u} of Nd ions placed at the surface of Nd{sub 2}Fe{sub 14}B grains. The results suggest the possibility that the A{sub 2}{sup 0} parameter of Nd ions at the (001) surface of Nd{sub 2}Fe{sub 14}B grains exhibits a negative value when the O or Cu atom is located near the surface, closer than its equilibrium position. At the (110) surface, however, O atoms located at the equilibrium position provide a negative A{sub 2}{sup 0}, while for Cu additions A{sub 2}{sup 0} remains positive regardless of Cu's position. Thus, Cu atoms are expected to maintain a positive local K{sub u} of surface Nd ions more frequently than O atoms when they approach the grain surfaces in the Nd-Fe-B grains.

  17. Tailor-made force fields for crystal-structure prediction.

    PubMed

    Neumann, Marcus A

    2008-08-14

    A general procedure is presented to derive a complete set of force-field parameters for flexible molecules in the crystalline state on a case-by-case basis. The force-field parameters are fitted to the electrostatic potential as well as to accurate energies and forces generated by means of a hybrid method that combines solid-state density functional theory (DFT) calculations with an empirical van der Waals correction. All DFT calculations are carried out with the VASP program. The mathematical structure of the force field, the generation of reference data, the choice of the figure of merit, the optimization algorithm, and the parameter-refinement strategy are discussed in detail. The approach is applied to cyclohexane-1,4-dione, a small flexible ring. The tailor-made force field obtained for cyclohexane-1,4-dione is used to search for low-energy crystal packings in all 230 space groups with one molecule per asymmetric unit, and the most stable crystal structures are reoptimized in a second step with the hybrid method. The experimental crystal structure is found as the most stable predicted crystal structure both with the tailor-made force field and the hybrid method. The same methodology has also been applied successfully to the four compounds of the fourth CCDC blind test on crystal-structure prediction. For the five aforementioned compounds, the root-mean-square deviations between lattice energies calculated with the tailor-made force fields and the hybrid method range from 0.024 to 0.053 kcal/mol per atom around an average value of 0.034 kcal/mol per atom. PMID:18642947

  18. Application of a rotating magnetic field to semiconductor crystal growth in Space

    NASA Astrophysics Data System (ADS)

    Senchenkov, A. S.; Barmin, I. V.

    2003-12-01

    To eliminate the tremendous influence of the residual accelerations on homogeneity of the crystal growing in a space experiment, a rotating magnetic field (RMF) is used. A number of the experiments have been performed in space within the RMF both in the frame of the Russian national program and together with European scientists. In the paper some theoretical and experimental results illustrating the effectiveness of RMF application to crystal growth under microgravity conditions are presented. Tables 2, Figs 5, Refs 8.

  19. Electron correlations in semiconductors: Bulk cohesive properties and magnetic-field-induced Wigner crystal at heterojunctions

    SciTech Connect

    Louie, S.G.; Zhu, X.

    1992-08-01

    A correlated wavefunction variational quantum Monte Carlo approach to the studies of electron exchange and correlation effects in semiconductors is presented. Applications discussed include the cohesive and structural properties of bulk semiconductors, and the magnetic-field-induced Wigner electron crystal in two dimensions. Landau level mixing is shown to be important in determining the transition between the quantum Hall liquid and the Wigner crystal states in the regime of relevant experimental parameters.

  20. Effects of Gravity on ZBLAN Glass Crystallization

    NASA Technical Reports Server (NTRS)

    Tucker, Dennis S.; Ethridge, Edwin C.; Smith, G. A.; Workman, G.

    2003-01-01

    The effects of gravity on the crystallization of ZrF4-BaF2-LaF3-AlF3- NaF glasses have been studied utilizing NASA's KC135 and a sounding rocket, Fibers and cylinders of ZBLAN glass were heated to the crystallization temperature in unit and reduced gravity. When processed in unit gravity the glass crystallized, but when processed in reduced gravity, crystallization was suppressed. A possible explanation involving shear thinning is presented to explain these results.

  1. Field Stability of Piezoelectric Shear Properties in PIN-PMN-PT Crystals Under Large Drive Field

    PubMed Central

    Zhang, Shujun; Li, Fei; Luo, Jun; Xia, Ru; Hackenberger, Wesley; Shrout, Thomas R.

    2013-01-01

    The coercive fields (EC) of Pb(In0.5Nb0.5)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) ternary single crystals were found to be 5 kV/cm, double the value of binary Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMNT) crystals, further increased to 6 to 9 kV/cm using Mn modifications. In addition to an increased EC, the acceptor modification resulted in the developed internal bias (Eint), on the order of ~1 kV/cm. The piezoelectric shear properties of unmodified and Mn-modified PIN-PMN-PT crystals with various domain configurations were investigated. The shear piezoelectric coefficients and electromechanical coupling factors for different domain configurations were found to be >2000 pC/N and >0.85, respectively, with slightly reduced properties observed in Mn-modified tetragonal crystals. Fatigue/cycling tests performed on shear-mode samples as a function of ac drive field level demonstrated that the allowable ac field levels (the maximum applied ac field before the occurrence of depolarization) were only ~2 kV/cm for unmodified crystals, less than half of their coercive field. Allowable ac drive levels were on the order of 4 to 6 kV/cm for Mn-modified crystals with rhombohedral/orthorhombic phase, further increased to 5 to 8 kV/cm in tetragonal crystals, because of their higher coercive fields. It is of particular interest that the allowable ac drive field level for Mn-modified crystals was found to be ≥60% of their coercive fields, because of the developed Eint, induced by the acceptor-oxygen vacancy defect dipoles. PMID:21342812

  2. Reorientation of single-wall carbon nanotubes in negative anisotropy liquid crystals by an electric field.

    PubMed

    García-García, Amanda; Vergaz, Ricardo; Algorri, José F; Zito, Gianluigi; Cacace, Teresa; Marino, Antigone; Otón, José M; Geday, Morten A

    2016-01-01

    Single-wall carbon nanotubes (SWCNT) are anisotropic nanoparticles that can cause modifications in the electrical and electro-optical properties of liquid crystals. The control of the SWCNT concentration, distribution and reorientation in such self-organized fluids allows for the possibility of tuning the liquid crystal properties. The alignment and reorientation of CNTs are studied in a system where the liquid crystal orientation effect has been isolated. Complementary studies including Raman spectroscopy, microscopic inspection and impedance studies were carried out. The results reveal an ordered reorientation of the CNTs induced by an electric field, which does not alter the orientation of the liquid crystal molecules. Moreover, impedance spectroscopy suggests a nonnegligible anchoring force between the CNTs and the liquid crystal molecules. PMID:27547599

  3. Reorientation of single-wall carbon nanotubes in negative anisotropy liquid crystals by an electric field

    PubMed Central

    García-García, Amanda; Vergaz, Ricardo; Algorri, José F; Zito, Gianluigi; Cacace, Teresa; Marino, Antigone; Otón, José M

    2016-01-01

    Summary Single-wall carbon nanotubes (SWCNT) are anisotropic nanoparticles that can cause modifications in the electrical and electro-optical properties of liquid crystals. The control of the SWCNT concentration, distribution and reorientation in such self-organized fluids allows for the possibility of tuning the liquid crystal properties. The alignment and reorientation of CNTs are studied in a system where the liquid crystal orientation effect has been isolated. Complementary studies including Raman spectroscopy, microscopic inspection and impedance studies were carried out. The results reveal an ordered reorientation of the CNTs induced by an electric field, which does not alter the orientation of the liquid crystal molecules. Moreover, impedance spectroscopy suggests a nonnegligible anchoring force between the CNTs and the liquid crystal molecules. PMID:27547599

  4. Lattice effects in YVO 3 single crystal

    NASA Astrophysics Data System (ADS)

    Marquina, C.; Sikora, M.; Ibarra, M. R.; Nugroho, A. A.; Palstra, T. T. M.

    2005-04-01

    In this paper we report on the lattice effects in the Mott insulator yttrium orthovanadate (YVO3). Linear thermal expansion and magnetostriction experiments have been performed on a single crystal, in the temperature range from 5 K to room temperature. The YVO3 orders antiferromagnetically at TN=116 K and orbital ordering was reported to appear below TOO=196 K. A first-order structural phase transition takes place at TS=77 K, accompanied by changes in the antiferromagnetic type of ordering as well as in the orbital-ordering type. Our results reveal that the thermal expansion measurement technique is a very powerful tool in order to clearly detect the existence of the above-mentioned transitions. The magnetostriction results point to the stability of the low-temperature-magnetic ground state under such high applied magnetic field.

  5. Effect of power arrangement on the crystal shape during the Kyropoulos sapphire crystal growth process

    NASA Astrophysics Data System (ADS)

    Chen, Chun-Hung; Chen, Jyh-Chen; Lu, Chung-Wei; Liu, Che-Ming

    2012-08-01

    The Kyropoulos (KY) method is commonly used to grow large sized sapphire single crystals. The shape of the sapphire crystal thus grown is determined by the heater arrangement and the power reduction history in the Kyropoulos furnace. In order to grow high-quality sapphire single crystal, the heater arrangement should allow different power inputs in different sections in order to control the thermal field in the melt during the growth process. In this study, a numerical computation is performed to investigate the effects of the heater arrangement on the thermal and flow transport, the shape of the crystal-melt interface, and the power requirements during the Kyropoulos sapphire crystal growth process in a resistance heated furnace. Four different power ratio arrangements in a three-zone heater are considered. The results show that for the power arrangements considered herein, the temperature gradients along the crystallization front do not exceed 0.05 K/mm, and that, after the growth of the crown, the crystal maintains an almost constant diameter. The remelting phenomenon may occur during growth when the input power of the upper side of the heater is higher than that of the lower side of the heater.

  6. Anisotropic local modification of crystal field levels in Pr-based pyrochlores: a muon-induced effect modeled using density functional theory.

    PubMed

    Foronda, F R; Lang, F; Möller, J S; Lancaster, T; Boothroyd, A T; Pratt, F L; Giblin, S R; Prabhakaran, D; Blundell, S J

    2015-01-01

    Although muon spin relaxation is commonly used to probe local magnetic order, spin freezing, and spin dynamics, we identify an experimental situation in which the measured response is dominated by an effect resulting from the muon-induced local distortion rather than the intrinsic behavior of the host compound. We demonstrate this effect in some quantum spin ice candidate materials Pr(2)B(2)O(7) (B=Sn, Zr, Hf), where we detect a static distribution of magnetic moments that appears to grow on cooling. Using density functional theory we show how this effect can be explained via a hyperfine enhancement arising from a splitting of the non-Kramers doublet ground states on Pr ions close to the muon, which itself causes a highly anisotropic distortion field. We provide a quantitative relationship between this effect and the measured temperature dependence of the muon relaxation and discuss the relevance of these observations to muon experiments in other magnetic materials. PMID:25615502

  7. A phase-field model coupled with lattice kinetics solver for modeling crystal growth in furnaces

    SciTech Connect

    Lin, Guang; Bao, Jie; Xu, Zhijie; Tartakovsky, Alexandre M.; Henager, Charles H.

    2014-02-02

    In this study, we present a new numerical model for crystal growth in a vertical solidification system. This model takes into account the buoyancy induced convective flow and its effect on the crystal growth process. The evolution of the crystal growth interface is simulated using the phase-field method. Two novel phase-field models are developed to model the crystal growth interface in vertical gradient furnaces with two temperature profile setups: 1) fixed wall temperature profile setup and 2) time-dependent temperature profile setup. A semi-implicit lattice kinetics solver based on the Boltzmann equation is employed to model the unsteady incompressible flow. This model is used to investigate the effect of furnace operational conditions on crystal growth interface profiles and growth velocities. For a simple case of macroscopic radial growth, the phase-field model is validated against an analytical solution. Crystal growth in vertical gradient furnaces with two temperature profile setups have been also investigated using the developed model. The numerical simulations reveal that for a certain set of temperature boundary conditions, the heat transport in the melt near the phase interface is diffusion dominant and advection is suppressed.

  8. Low-field susceptibility anisotropy of some biotite crystals

    NASA Astrophysics Data System (ADS)

    Zapletal, Karel

    1990-10-01

    The low-field magnetic susceptibility anisotropy (LMA) of weakly magnetic rocks is dominated by paramagnetic minerals among which micas, and mainly biotite, is important. For this reason, the LMA of biotite crystals was investigated in detail. Natural biotite crystals (from ten localities) having a wide range of iron concentration were also studied by other methods, including optical microscopy, X-ray microanalysis, Mössbauer spectroscopy and induced isothermal remanent magnetization. Ferromagnetic inclusions disturbing the magnetic properties of biotite were revealed in some crystals. The measured mean bulk susceptibility of pure crystals (four localities) ranges from 1.0 × 10 -3 to 1.8 × 10 -3 SI and agrees with the susceptibility calculated from the iron concentration (ranging from 12 to 20 wt.%) determined for each specimen. The susceptibility ellipsoid of pure biotite crystals is rotational about the minimum susceptibility direction parallel to the crystallographic c'-axis, and the anisotropy degree ranges from 1.34 to 1.36.

  9. Magnetic field controlled FZ single crystal growth of intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Hermann, R.; Behr, G.; Gerbeth, G.; Priede, J.; Uhlemann, H.-J.; Fischer, F.; Schultz, L.

    2005-02-01

    Intermetallic rare-earth-transition-metal compounds with their coexistence of magnetic ordering and superconductivity are still of great scientific interest. The crystal growth of bulk single crystals is very often unsuccessful due to an unfavorable solid-liquid interface geometry enclosing concave fringes. The aim of the work is the contactless control of heat and material transport during floating-zone single crystal growth of intermetallic compounds. This control is provided by a tailored design of the electromagnetic field and the resulting electromagnetically driven convection. Numerical simulations for the determination of the electromagnetic field configuration induced by the RF heater coil and the solution of the coupled heat and hydrodynamic equations were done for the model substance Ni with and without additional magnetic field. As a result, an innovative magnetic two-phase stirrer system has been developed which enables the controlled influence on the melt ranging from intensive inwards/outwards flows to flows almost at rest. The selection of parameters necessary for the desired fluid flow is determined from numerical simulation. The basis for the calculations are the process-related fluid flow conditions which are determined by the mode of heating, heat radiation at the free surface and material parameters. This treatment of the problem leads to the customised magnetic field for the special intermetallic compound. The application of the new magnetic system leads to a distinct improvement of the solid-liquid interface validated on experiments with the model substance Nickel.

  10. 3D crack tip fields for FCC single crystals

    SciTech Connect

    Cuitino, A.M.; Ortiz, M.

    1995-12-31

    Cracks in single crystals are of concern in a number of structural and non-structural applications, ranging form single-crystal turbine blades and rotors to metal interconnect lines in microcircuits. In this paper we present 3D numerical simulations of the crack-tip fields of a Cu single crystal, including stress, strain and slip activity patterns. The orientation of the crack tip is along the crystallographic orientation (101), while the crack plane is (010). A material model based on dislocation mechanics is used in these simulations. This model correctly predicts the observed behavior of Cu, including the basic hardening characteristics of single crystals, orientation dependence and stage I-II-III structure of the stress-strain curves, the observed levels of latent hardening and their variation with orientation and deformation in the primary system and slip activities and dislocation densities. We use the FEM within the context of finite deformation plasticity. In the figure below, we show the finite element mesh composed by 12-noded tetrahedrons with 6-noded triangular faces. The model simulates half of a beam, which is subjected to a concentrated load at 1/8 of total length from the support. Detailed results of the stress, deformation and slip activity are presented at different radii from crack tip and at different depths from the surface. In general, the results show a strong difference in the slip activity pattern form the interior to the exterior, while smaller differences are encountered in the stress and strain fields.

  11. Self-Aligned Growth of Organic Semiconductor Single Crystals by Electric Field.

    PubMed

    Kotsuki, Kenji; Obata, Seiji; Saiki, Koichiro

    2016-01-19

    We proposed a novel but facile method for growing organic semiconductor single-crystals via solvent vapor annealing (SVA) under electric field. In the conventional SVA growth process, nuclei of crystals appeared anywhere on the substrate and their crystallographic axes were randomly distributed. We applied electric field during the SVA growth of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) on the SiO2/Si substrate on which a pair of electrodes had been deposited beforehand. Real-time observation of the SVA process revealed that rodlike single crystals grew with their long axes parallel to the electric field and bridged the prepatterned electrodes. As a result, C8-BTBT crystals automatically formed a field effect transistor (FET) structure and the mobility reached 1.9 cm(2)/(V s). Electric-field-assisted SVA proved a promising method for constructing high-mobility single-crystal FETs at the desired position by a low-cost solution process. PMID:26695105

  12. Influence of electromagnetic field intensity on the metastable zone width of CaCO3 crystallization in circulating water

    NASA Astrophysics Data System (ADS)

    Wang, Jianguo; Liang, Yandong; Chen, Si

    2016-09-01

    In this study, changes in the metastable zone width of CaCO3 crystallization was determined through conductivity titration by altering electromagnetic field parameters applied to the circulating water system. The critical conductivity value and metastable zone curves of CaCO3 crystallization were determined under different solution concentrations and electromagnetic field intensities. Experimental results indicate that the effect of the electromagnetic field intensity on the critical conductivity value intensifies with the increase of solution concentration. Moreover, the metastable zone width of CaCO3 crystallization increases with the increase of electromagnetic field intensity within 200 Gs, thereby prolonging the induction period of nucleation.

  13. Field-induced phase transitions in chiral smectic liquid crystals studied by the constant current method

    NASA Astrophysics Data System (ADS)

    H, Dhaouadi; R, Zgueb; O, Riahi; F, Trabelsi; T, Othman

    2016-05-01

    In ferroelectric liquid crystals, phase transitions can be induced by an electric field. The current constant method allows these transition to be quickly localized and thus the (E,T) phase diagram of the studied product can be obtained. In this work, we make a slight modification to the measurement principles based on this method. This modification allows the characteristic parameters of ferroelectric liquid crystal to be quantitatively measured. The use of a current square signal highlights a phenomenon of ferroelectric hysteresis with remnant polarization at null field, which points out an effect of memory in this compound.

  14. Low-frequency electromagnetic field in a Wigner crystal

    SciTech Connect

    Stupka, Anton

    2013-03-15

    Long-wave low-frequency oscillations are described in a Wigner crystal by generalization of the reverse continuum model for the case of electronic lattice. The internal self-consistent long-wave electromagnetic field is used to describe the collective motions in the system. The eigenvectors and eigenvalues of the obtained system of equations are derived. The velocities of longitudinal and transversal sound waves are found.

  15. Convection effects in protein crystal growth

    NASA Technical Reports Server (NTRS)

    Roberts, Glyn O.

    1988-01-01

    Protein crystals for X-ray diffraction study are usually grown resting on the bottom of a hanging drop of a saturated protein solution, with slow evaporation to the air in a small enclosed cell. The evaporation rate is controlled by hanging the drop above a reservoir of water, with its saturation vapor pressure decreased by a low concentration of a passive solute. The drop has a lower solute concentration, and its volume shrinks by evaporation until the molecular concentrations match. Protein crystals can also be grown from a seed crystal suspended or supported in the interior of a supersaturated solution. The main analysis of this report concerns this case because it is less complicated than hanging-drop growth. Convection effects have been suggested as the reason for the apparent cessation of growth at a certain rather small crystal size. It seeems that as the crystal grows, the number of dislocations increases to a point where further growth is hindered. Growth in the microgravity environment of an orbiting space vehicle has been proposed as a method for obtaining larger crystals. Experimental observations of convection effects during the growth of protein crystals have been reported.

  16. Plasticity and dislocation dynamics in a phase field crystal model.

    PubMed

    Chan, Pak Yuen; Tsekenis, Georgios; Dantzig, Jonathan; Dahmen, Karin A; Goldenfeld, Nigel

    2010-07-01

    The critical dynamics of dislocation avalanches in plastic flow is examined using a phase field crystal model. In the model, dislocations are naturally created, without any ad hoc creation rules, by applying a shearing force to the perfectly periodic ground state. These dislocations diffuse, interact and annihilate with one another, forming avalanche events. By data collapsing the event energy probability density function for different shearing rates, a connection to interface depinning dynamics is confirmed. The relevant critical exponents agree with mean field theory predictions. PMID:20867460

  17. Surface mediated nonlinear optic effects in liquid crystals

    NASA Astrophysics Data System (ADS)

    Merlin, Jessica M.

    Liquid crystals have become a significant part of technology, mainly through their use in the display industry. This is due in part to the fact that the optical properties of liquid crystals are easily manipulated electronically. It has been recognized that the optical properties liquid crystals may also be controlled using light. Because of this, there are other various applications being explored for liquid crystals in photorefraction, optical limiting and switching, and in spatial light modulators. Although, the photorefractive effect was reported in liquid crystals over 10 years ago, there is still controversy over the exact mechanism for the reorientation of the liquid crystal director. This difficulty may be due in part to the fact that it is difficult to characterize the effect using photorefractive measurements and figures of merit. The optical and electronic control of liquid crystals will be studied here using a Friedericksz transition measurement in a twist cell geometry. This type of apparatus was chosen because it leads to a more direct demonstration of the surface effect. Namely, by studying changes in the Friedericksz transition threshold in a twist cell, a more direct observation of changes in the internal field may be observed. First a brief introduction to liquid crystals and their role in technology will be presented. This will be followed by a more rigorous discussion of the physics of liquid crystals and a review of the important literature. The experimental apparatus and the materials and cell geometry used will be described followed by the results of those measurements. Finally, the results will be considered in terms of a model involving interfacial charge and discussed in the context of previous work.

  18. Effect of Interaction of the Temperature Field and Supersaturation on the Morphology of the Solid-Vapor Interface in Crystal Growth by Physical Vapor Transport

    NASA Technical Reports Server (NTRS)

    Grasza, K.; Palosz, W.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    An in-situ study of the morphology of the solid-vapor interface during iodine crystal growth was done. The conditions for terrace growth, flat faces formation and retraction, competition between sources of steps, formation of protrusions, surface roughening, and defect overgrowth are demonstrated and discussed.

  19. Crystal field parameters and energy levels scheme of trivalent chromium doped BSO

    NASA Astrophysics Data System (ADS)

    Petkova, P.; Andreici, E.-L.; Avram, N. M.

    2014-11-01

    The aim of this paper is to give an analysis of crystal field parameters and energy levels schemes for the above doped material, in order to give a reliable explanation for experimental data. The crystal field parameters have been modeled in the frame of Exchange Charge Model (ECM) of the crystal field theory, taken into account the geometry of systems, with actually site symmetry of the impurity ions. The effect of the charges of the ligands and covalence bonding between chromium cation and oxygen anions, in the cluster approach, also were taken into account. With the obtained values of the crystal field parameters we simulated the scheme of energy levels of chromium ions by diagonalizing the matrix of the Hamiltonian of the doped crystal. The obtained energy levels and estimated Racah parameters B and C were compared with the experimental spectroscopic data and discussed. Comparison with experiment shows that the results are quite satisfactory which justify the model and simulation scheme used for the title system.

  20. Crystal field parameters and energy levels scheme of trivalent chromium doped BSO

    SciTech Connect

    Petkova, P.; Andreici, E.-L.; Avram, N. M.

    2014-11-24

    The aim of this paper is to give an analysis of crystal field parameters and energy levels schemes for the above doped material, in order to give a reliable explanation for experimental data. The crystal field parameters have been modeled in the frame of Exchange Charge Model (ECM) of the crystal field theory, taken into account the geometry of systems, with actually site symmetry of the impurity ions. The effect of the charges of the ligands and covalence bonding between chromium cation and oxygen anions, in the cluster approach, also were taken into account. With the obtained values of the crystal field parameters we simulated the scheme of energy levels of chromium ions by diagonalizing the matrix of the Hamiltonian of the doped crystal. The obtained energy levels and estimated Racah parameters B and C were compared with the experimental spectroscopic data and discussed. Comparison with experiment shows that the results are quite satisfactory which justify the model and simulation scheme used for the title system.

  1. Discrete dislocation plasticity and crack tip fields in single crystals

    NASA Astrophysics Data System (ADS)

    Van der Giessen, E.; Deshpande, V. S.; Cleveringa, H. H. M.; Needleman, A.

    2001-09-01

    Small-scale yielding around a stationary plane strain mode I crack is analyzed using discrete dislocation plasticity. The dislocations are all of edge character, and are modeled as line singularities in a linear elastic material. Superposition is used to represent the solution in terms of analytical fields for edge dislocations in a half-space and a numerical image solution that enforces the boundary conditions. The description of the dislocation dynamics includes the lattice resistance to dislocation motion, dislocation nucleation, interaction with obstacles and annihilation. A model planar crystal with three slip systems is considered. Two slip system orientations are analyzed that differ by a 90° rotation. The non-hardening, single crystal plasticity continuum slip solution of Rice (Mech. Mater. 6 (1987) 317) for this model crystal predicts that slip and kink bands emerge for both crystal geometries, while Drugan (J. Mech. Phys. Solids 49 (2001) 2155) has obtained kink band free solutions. For a reference set of parameter values, kink band free solutions are found in one orientation while the emergence of kink bands is seen in the other orientation. However, lowering the dislocation source density suppresses the formation of kink bands in this orientation as well. In all calculations, the opening stress in the immediate vicinity of the crack tip is much larger than predicted by continuum slip theory.

  2. An optimized intermolecular force field for hydrogen-bonded organic molecular crystals using atomic multipole electrostatics.

    PubMed

    Pyzer-Knapp, Edward O; Thompson, Hugh P G; Day, Graeme M

    2016-08-01

    We present a re-parameterization of a popular intermolecular force field for describing intermolecular interactions in the organic solid state. Specifically we optimize the performance of the exp-6 force field when used in conjunction with atomic multipole electrostatics. We also parameterize force fields that are optimized for use with multipoles derived from polarized molecular electron densities, to account for induction effects in molecular crystals. Parameterization is performed against a set of 186 experimentally determined, low-temperature crystal structures and 53 measured sublimation enthalpies of hydrogen-bonding organic molecules. The resulting force fields are tested on a validation set of 129 crystal structures and show improved reproduction of the structures and lattice energies of a range of organic molecular crystals compared with the original force field with atomic partial charge electrostatics. Unit-cell dimensions of the validation set are typically reproduced to within 3% with the re-parameterized force fields. Lattice energies, which were all included during parameterization, are systematically underestimated when compared with measured sublimation enthalpies, with mean absolute errors of between 7.4 and 9.0%. PMID:27484370

  3. An optimized intermolecular force field for hydrogen-bonded organic molecular crystals using atomic multipole electrostatics

    PubMed Central

    Pyzer-Knapp, Edward O.; Thompson, Hugh P. G.; Day, Graeme M.

    2016-01-01

    We present a re-parameterization of a popular intermolecular force field for describing intermolecular interactions in the organic solid state. Specifically we optimize the performance of the exp-6 force field when used in conjunction with atomic multipole electrostatics. We also parameterize force fields that are optimized for use with multipoles derived from polarized molecular electron densities, to account for induction effects in molecular crystals. Parameterization is performed against a set of 186 experimentally determined, low-temperature crystal structures and 53 measured sublimation enthalpies of hydrogen-bonding organic molecules. The resulting force fields are tested on a validation set of 129 crystal structures and show improved reproduction of the structures and lattice energies of a range of organic molecular crystals compared with the original force field with atomic partial charge electrostatics. Unit-cell dimensions of the validation set are typically reproduced to within 3% with the re-parameterized force fields. Lattice energies, which were all included during parameterization, are systematically underestimated when compared with measured sublimation enthalpies, with mean absolute errors of between 7.4 and 9.0%. PMID:27484370

  4. Transverse magnetic field impact on waveguide modes of photonic crystals.

    PubMed

    Sylgacheva, Daria; Khokhlov, Nikolai; Kalish, Andrey; Dagesyan, Sarkis; Prokopov, Anatoly; Shaposhnikov, Alexandr; Berzhansky, Vladimir; Nur-E-Alam, Mohammad; Vasiliev, Mikhail; Alameh, Kamal; Belotelov, Vladimir

    2016-08-15

    This Letter presents a theoretical and experimental study of waveguide modes of one-dimensional magneto-photonic crystals magnetized in the in-plane direction. It is shown that the propagation constants of the TM waveguide modes are sensitive to the transverse magnetization and the spectrum of the transverse magneto-optical Kerr effect has resonant features at mode excitation frequencies. Two types of structures are considered: a non-magnetic photonic crystal with an additional magnetic layer on top and a magneto-photonic crystal with a magnetic layer within each period. We found that the magneto-optical non-reciprocity effect is greater in the first case: it has a magnitude of δ∼10-4, while the second structure type demonstrates δ∼10-5 only, due to the higher asymmetry of the claddings of the magnetic layer. Experimental observations show resonant features in the optical and magneto-optical Kerr effect spectra. The measured dispersion properties are in good agreement with the theoretical predictions. An amplitude of light intensity modulation of up to 2.5% was observed for waveguide mode excitation within the magnetic top layer of the non-magnetic photonic crystal structure. The presented theoretical approach may be utilized for the design of magneto-optical sensors and modulators requiring pre-determined spectral features. PMID:27519096

  5. Long-range orientational order, local-field anisotropy, and mean molecular polarizability in liquid crystals

    SciTech Connect

    Aver'yanov, E. M.

    2009-01-15

    The problems on the relation of the mean effective molecular polarizability {gamma}-bar to the long-range orientational order of molecules (the optical anisotropy of the medium) in uniaxial and biaxial liquid crystals, the local anisotropy on mesoscopic scales, and the anisotropy of the Lorentz tensor L and the local-field tensor f are formulated and solved. It is demonstrated that the presence of the long-range orientational order of molecules in liquid crystals imposes limitations from below on the molecular polarizability {gamma}-bar, which differs for uniaxial and biaxial liquid crystals. The relation between the local anisotropy and the molecular polarizability {gamma}-bar is investigated for calamitic and discotic uniaxial liquid crystals consisting of lath- and disk-shaped molecules. These liquid crystals with identical macroscopic symmetry differ in the local anisotropy and the relationships between the components L{sub parallel} < L{sub perpendicular} , f{sub parallel} < f{sub perpendicular} (calamitic) and L{sub parallel} > L{sub perpendicular} , f{sub parallel} > f{sub perpendicular} (discotic) for an electric field oriented parallel and perpendicular to the director. The limitations from below and above on the molecular polarizability {gamma}-bar due to the anisotropy of the tensors L and f are established for liquid crystals of both types. These limitations indicate that the molecular polarizability {gamma}-bar depends on the phase state and the temperature. The factors responsible for the nonphysical consequences of the local-field models based on the approximation {gamma}-bar = const are revealed. The theoretical inferences are confirmed by the experimental data for a number of calamitic nematic liquid crystals with different values of birefringence and the discotic liquid crystal Col{sub ho}.

  6. AOM reconciling of crystal field parameters for UCl sub 3 , UBr sub 3 , Ul sub 3 series

    SciTech Connect

    Gajek, Z.; Mulak, J. )

    1990-07-01

    Available inelastic neutron scattering interpretations of crystal field effect in the uranium trihalides have been verified in terms of Angular Overlap Model. For UCl{sub 3} a good reconciling of both INS and optical interpretations of crystal field effect has been obtained. On the contrary, the parameterizations for UBr{sub 3} and UI{sub 3} were found to be highly artificial and suggestion is given to experimentalists to reinterpret their INS spectra.

  7. Travelling magnetic fields applied to bulk crystal growth from the melt: The step from basic research to industrial scale

    NASA Astrophysics Data System (ADS)

    Rudolph, Peter

    2008-04-01

    After introduction of various types of magnetic fields in crystal growth, their main pros and cons for crystallization processes are discussed. It is shown that their further developments towards industrial maturity are bound up with the cardinal demands—increase of the process output, improvement of the crystal quality, and reduction of costs. In a further section, the advantages of travelling magnetic fields are presented. The central chapter is devoted to the target of the current KRISTMAG˜ project—the development of an internal heater-magnet module for coupled generation of temperature and a travelling magnetic field, suitable for incorporation into industrial Czochralski pullers and vertical gradient freeze equipments. Amplitude, frequency and phase shift of the three-phase current are all adjustable and are combined with a dc component to control the crystallization process effectively. Results of accompanying numeric modelling are presented. The current state of crystal growth experiments in travelling magnetic field and first encouraging results are given.

  8. An unforeseen polymorph of coronene by the application of magnetic fields during crystal growth

    NASA Astrophysics Data System (ADS)

    Potticary, Jason; Terry, Lui R.; Bell, Christopher; Papanikolopoulos, Alexandros N.; Christianen, Peter C. M.; Engelkamp, Hans; Collins, Andrew M.; Fontanesi, Claudio; Kociok-Köhn, Gabriele; Crampin, Simon; da Como, Enrico; Hall, Simon R.

    2016-05-01

    The continued development of novel drugs, proteins, and advanced materials strongly rely on our ability to self-assemble molecules in solids with the most suitable structure (polymorph) in order to exhibit desired functionalities. The search for new polymorphs remains a scientific challenge, that is at the core of crystal engineering and there has been a lack of effective solutions to this problem. Here we show that by crystallizing the polyaromatic hydrocarbon coronene in the presence of a magnetic field, a polymorph is formed in a β-herringbone structure instead of the ubiquitous γ-herringbone structure, with a decrease of 35° in the herringbone nearest neighbour angle. The β-herringbone polymorph is stable, preserves its structure under ambient conditions and as a result of the altered molecular packing of the crystals, exhibits significant changes to the optical and mechanical properties of the crystal.

  9. An unforeseen polymorph of coronene by the application of magnetic fields during crystal growth

    PubMed Central

    Potticary, Jason; Terry, Lui R.; Bell, Christopher; Papanikolopoulos, Alexandros N.; Christianen, Peter C. M.; Engelkamp, Hans; Collins, Andrew M.; Fontanesi, Claudio; Kociok-Köhn, Gabriele; Crampin, Simon; Da Como, Enrico; Hall, Simon R.

    2016-01-01

    The continued development of novel drugs, proteins, and advanced materials strongly rely on our ability to self-assemble molecules in solids with the most suitable structure (polymorph) in order to exhibit desired functionalities. The search for new polymorphs remains a scientific challenge, that is at the core of crystal engineering and there has been a lack of effective solutions to this problem. Here we show that by crystallizing the polyaromatic hydrocarbon coronene in the presence of a magnetic field, a polymorph is formed in a β-herringbone structure instead of the ubiquitous γ-herringbone structure, with a decrease of 35° in the herringbone nearest neighbour angle. The β-herringbone polymorph is stable, preserves its structure under ambient conditions and as a result of the altered molecular packing of the crystals, exhibits significant changes to the optical and mechanical properties of the crystal. PMID:27161600

  10. Entropy changes and caloric effects in RAl2 single crystals

    NASA Astrophysics Data System (ADS)

    Antunes de Oliveira, Nilson; Caro Patiño, Julieth; von Ranke, Pedro R.

    2015-03-01

    In this work we theoretically discuss the entropy changes and the caloric effects in RAl2 single crystals, which crystalize in the cubic symmetry and have large magneto crystalline anisotropy due to the crystal electric field. For this purpose, we use a model of interacting magnetic moments including a term to account for the crystal electric field. We apply the model to calculate the entropy changes and the magnetocaloric quantities in TmAl2 and NdAl2 by applying magnetic field variations in different crystallographic directions. Our calculations for the entropy changes in these compounds are in a reasonable agreement with the available experimental data for ΔB = 7 T. Further experimental data are necessary to compare with our theoretical predictions for the adiabatic temperature change. We also calculate the caloric quantities by fixing the magnitude of the magnetic field and rotating its direction. In this case, our calculations predict an anomaly (i.e. a change of sign) in the caloric quantities of TmAl2 when a magnetic field of 3 T rotates from < 100 > to < 110 > direction. A similar behavior is also observed in NdAl2. This very interesting fact, which is basically due to the magneto crystalline anisotropy, needs experimental data to be confirmed CNPq, CAPES, FAPERJ.

  11. Low-Temperature Band Transport and Impact of Contact Resistance in Organic Field-Effect Transistors Based on Single-Crystal Films of Ph-BTBT-C10

    NASA Astrophysics Data System (ADS)

    Cho, Joung-min; Mori, Takehiko

    2016-06-01

    Transistors based on single-crystal films of 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10) fabricated using the blade-coating method are investigated by the four-probe method down to low temperatures. The four-probe mobility is as large as 18 cm2/V s at room temperature, and increases to 45 cm2/V s at 80 K. At 60 K the two-probe mobility drops abruptly by about 50%, but the mobility drop is mostly attributed to the increase of the source resistance. The carrier transport in the present single-crystal film is regarded as essentially bandlike down to 30 K.

  12. Bridgman Growth of Germanium Crystals in a Rotating Magnetic Field

    NASA Technical Reports Server (NTRS)

    Volz, M. P.; Szofran, F. R.; Cobb, S. D.; Schweizer, M.; Walker, J. S.

    2005-01-01

    A series of (100)-oriented gallium-doped germanium crystals has been grown by the vertical Bridgman method and under the influence of a rotating magnetic field (RMF). Time-dependent flow instabilities occur when the critical magnetic Taylor number (Tm(sup c)) is exceeded, and this can be observed by noting the appearance of striations in the grown crystals. Tm(sup c) decreases as the aspect ratio of the melt increases, and approaches the theoretical limit expected for an infinite cylinder. Intentional interface demarcations are introduced by pulsing the RMF on and off The RMF has a marked affect on the interface shape, changing it from concave to nearly flat as the RMF strength is increased.

  13. Bridgman Growth of Germanium Crystals in a Rotating Magnetic Field

    NASA Technical Reports Server (NTRS)

    Volz, M. P.; Walker, J. S.; Schweizer, M.; Cobb, S. D.; Szofran, F. R.

    2004-01-01

    A series of (100)-oriented gallium-doped germanium crystals have been grown by the Bridgman method and under the influence of a rotating magnetic field (RMF). Time-dependent flow instabilities occur when the critical magnetic Taylor number (Tm(sup c) is exceeded, and this can be observed by noting the appearance of striations in the grown crystals. The experimental data indicate that Tm(sup c) increases as the aspect ratio of the melt decreases. Modeling calculations predicting Tm(sup c) as a function of aspect ratio are in reasonable agreement with the experimental data. The RMF has a marked affect on the interface shape, changing it from concave to nearly flat as the RMF strength is increased. Also, by pulsing the RMF on and off, it is shown that intentional interface demarcations can be introduced.

  14. Portable piezoelectric crystal detector for field monitoring of environmental pollutants

    SciTech Connect

    Ho, M.H.; Guilbault, G.G.; Rietz, B.

    1983-09-01

    A portable field monitor was constructed by using a coated piezoelectric crystal for direct monitoring of toluene in a Danish printing plant. Toluene vapor was adsorbed onto the Pluronic F-68 coating on a quartz crystal and a decrease in frequency was observed. Various substances which could interfere with toluene determination were tested. No interference from CO, NH/sub 3/, SO/sub 2/, HCl at 100 ppm are expected. Water vapor interfered and was selectively removed using a Nafion permeation tube. The readings from the piezoelectric detector were compared to two accepted procedures for monitoring toluene, the photoionization detector and the Drager tube. Results indicate that the piezoelectric detector gave data consistent with both other methods and with better relative standard deviations than the other two. 8 references, 2 figures, 1 table.

  15. Study of Fluid Flow Control in Protein Crystallization using Strong Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Ramachandran, Narayanan; Leslie, Fred; Ciszak, Ewa

    2002-11-01

    positioning the crystal growth cell so that the magnetic susceptibility force counteracts terrestrial gravity. The general objective is to test the hypothesis of convective control using a strong magnetic field and magnetic field gradient and to understand the nature of the various forces that come into play. Specifically we aim to delineate causative factors and to quantify them through experiments, analysis and numerical modeling. Once the basic understanding is obtained, the study will focus on testing the hypothesis on proteins of pyruvate dehydrogenase complex (PDC), proteins E1 and E3. Obtaining high crystal quality of these proteins is of great importance to structural biologists since their structures need to be determined. Specific goals for the investigation are: 1. To develop an understanding of convection control in diamagnetic fluids with concentration gradients through experimentation and numerical modeling. Specifically solutal buoyancy driven convection due to crystal growth will be considered. 2. To develop predictive measures for successful crystallization in a magnetic field using analyses and numerical modeling for use in future protein crystal growth experiments. This will establish criteria that can be used to estimate the efficacy of magnetic field flow damping on crystallization of candidate proteins. 3. To demonstrate the understanding of convection damping by high magnetic fields to a class of proteins that is of interest and whose structure is as yet not determined. 4. To compare quantitatively, the quality of the grown crystals with and without a magnetic field. X-ray diffraction techniques will be used for the comparative studies. In a preliminary set of experiments, we studied crystal dissolution effects in a 5 Tesla magnet available at NASA Marshall Space Flight Center (MSFC). Using a Schlieren setup, a 1mm crystal of Alum (Aluminum-Potassium Sulfate) was introduced in a 75% saturated solution and the resulting dissolution plume was observed

  16. Study of Fluid Flow Control in Protein Crystallization using Strong Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Ramachandran, Narayanan; Leslie, Fred; Ciszak, Ewa

    2002-01-01

    positioning the crystal growth cell so that the magnetic susceptibility force counteracts terrestrial gravity. The general objective is to test the hypothesis of convective control using a strong magnetic field and magnetic field gradient and to understand the nature of the various forces that come into play. Specifically we aim to delineate causative factors and to quantify them through experiments, analysis and numerical modeling. Once the basic understanding is obtained, the study will focus on testing the hypothesis on proteins of pyruvate dehydrogenase complex (PDC), proteins E1 and E3. Obtaining high crystal quality of these proteins is of great importance to structural biologists since their structures need to be determined. Specific goals for the investigation are: 1. To develop an understanding of convection control in diamagnetic fluids with concentration gradients through experimentation and numerical modeling. Specifically solutal buoyancy driven convection due to crystal growth will be considered. 2. To develop predictive measures for successful crystallization in a magnetic field using analyses and numerical modeling for use in future protein crystal growth experiments. This will establish criteria that can be used to estimate the efficacy of magnetic field flow damping on crystallization of candidate proteins. 3. To demonstrate the understanding of convection damping by high magnetic fields to a class of proteins that is of interest and whose structure is as yet not determined. 4. To compare quantitatively, the quality of the grown crystals with and without a magnetic field. X-ray diffraction techniques will be used for the comparative studies. In a preliminary set of experiments, we studied crystal dissolution effects in a 5 Tesla magnet available at NASA Marshall Space Flight Center (MSFC). Using a Schlieren setup, a 1mm crystal of Alum (Aluminum-Potassium Sulfate) was introduced in a 75% saturated solution and the resulting dissolution plume was observed

  17. Statistical mechanics of the flexoelectric effect in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Dhakal, Subas; Selinger, Jonathan V.

    2009-03-01

    Flexoelectricity is the phenomenon in which polarization is induced by imposed deformations of the director field in nematic liquid crystals. Recent experiments [1,2] have found that the flexoelectric effect is three orders of magnitude greater for bent-core liquid crystals than for conventional rod-like liquid crystals. To understand this experimental result, we develop a lattice model for the statistical mechanics of the flexoelectric effect. We perform Monte Carlo simulations and mean-field calculations to find the behavior as a function of interaction parameters, temperature, and applied electric field. The resulting phase diagram has four phases: isotropic, uniaxial nematic, biaxial nematic, and polar. In the uniaxial and biaxial nematic phases, there is a large splay or bend flexoelectric effect, which diverges as the system approaches the nematic-polar transition. This model may explain the large bend flexoelectric coefficient observed in bent-core liquid crystals, which have a tendency toward polar order. [1] J. Harden, B. Mbanga, N. Eber, K. Fodor-Csorba, S. Sprunt, J. T. Gleeson, and A. Jakli, Phys. Rev. Lett. 97,157802 (2006). [2] J. Harden, R. Teeling, J. T. Gleeson, S. Sprunt, and A.Jakli, Phys. Rev. E 78, 031702 (2008).

  18. A phase-field/Monte-Carlo model describing organic crystal growth from solution. Investigation of the diffusion-influenced growth of hydroquinone crystals

    NASA Astrophysics Data System (ADS)

    Kundin, J.; Yürüdü, C.; Ulrich, J.; Emmerich, H.

    2009-08-01

    In this paper work we present a phase-field/Monte-Carlo hybrid algorithm for the simulation of solutal growth of organic crystals. The algorithm is subsequently used for an investigation of diffusion effects on the growth mechanisms. This method combines a two-scale phase-field model of the liquid phase epitaxial growth and a Monte-Carlo algorithm of the 2D nucleation and thus is faster than previous purely Monte Carlo simulations of crystal growth. The inclusion of supersaturation and diffusion in the method allows the study of crystal growth under various growth conditions. Parameters used in the hybrid algorithm are bound to the energetic parameters of crystal faces, which can be estimated from a detailed study of the actual crystal structure based on a connected nets analysis, which allows the prediction of the shape and morphology of real crystals. The study of the diffusion effect is carried out based on an example of a hydroquinone crystal, which grows from the water solution at various supersaturations. The dependencies of the growth rate and the nucleation rate on the supersaturation indicate the change of the growth mechanism from spiral growth to 2D nucleation. The difference in the growth rate for various faces is in agreement with the crystal morphologies derived from the attachment energy method and observed experimentally. The main result of the simulation is the evaluation of engineering limits for choosing appropriate external process conditions.

  19. Large area mode field photonic crystal fiber design

    NASA Astrophysics Data System (ADS)

    Guo, Shuqin; An, Wensheng; Wang, Kang; Zhu, Guangxin; Le, Zichun

    2005-11-01

    A novel design method about photonic crystal fiber (PCF) with large area model field (LAMF) is demonstrated. Different from ordinarily design that the core of PCF formed by missing one air holes in the center of section, many air holes distributed in heartland all together come into being the core region. Air holes are arranged regularly in core region and outer cladding regions according to different periodical character, respectively. The effective refractive index (n eff ) of core region should be higher than cladding region because of total internal reflection (TIR) requirement. In this paper, two kinds of typical scheme are offered to realize LAMF-PCF. First, Λ, the spacing of neighboring air holes in whole section is fixed, once the radius of air holes in the core region r c is smaller than the cladding air holes r cla, LAMF-PCF will be formed. The modal area only lessens a little as r c is reduced. Especially, optimal size of r c can nearly make MFA insensitive to wavelength. On the contrary, dispersion parameter of PCF will take place visible change along with r c reduced, and ultra-flattened dispersion character can be realized when r c is optimized. Another method of designing LAMF-PCF is keeping all air holes uniform in the whole section of PCF, but the space of neighboring air holes in the core region Λ c is longer than the cladding region Λ cla, so n eff of core region is higher than the cladding region and TIR can take place.

  20. Electric-field-induced weakly chaotic transients in ferroelectric liquid crystals.

    PubMed

    Śliwa, I; Jeżewski, W; Kuczyński, W

    2016-01-01

    Nonlinear dynamics induced in surface stabilized ferroelectric liquid crystals by strong alternating external electric fields is studied both theoretically and experimentally. As has already been shown, molecular reorientations induced by sufficiently strong fields of high-enough frequencies can reveal a long transient behavior that has a weakly chaotic character. The resulting complex dynamics of ferroelectric liquid crystals can be considered not only as a consequence of irregular motions of particular molecules but also as a repercussion of a surface-enforced partial decorrelation of nonlinear molecular motions within smectic layers. To achieve more insight into the nature of this phenomenon and to show that the underlying complex field-induced behavior of smectic liquid crystals is not exceptional, ranges of system parameters for which the chaotic behavior occurs are determined. It is proved that there exists a large enough set of initial phase trajectory points, for which weakly chaotic long-time transitory phenomena occur, and, thereby, it is demonstrated that such a chaotic behavior can be regarded as being typical for strongly field-driven thin liquid crystal systems. Additionally, the influence of low-amplitude random noise on the duration of the transient processes is numerically studied. The strongly nonlinear contribution to the electro-optic response, experimentally determined for liquid crystal samples at frequencies lower than the actual field frequency, is also analyzed for long-time signal sequences. Using a statistical approach to distinguish numerically response signals of samples from noise generated by measuring devices, it is shown that the distribution of sample signals distinctly differs from the device noise. This evidently corroborates the occurrence of the nonlinear low-frequency effect, found earlier for different surface stabilized liquid crystal samples. PMID:26871130

  1. Vibronic spectra of U4 in octahedral crystal fields

    NASA Astrophysics Data System (ADS)

    Flint, C. D.; Tanner, P. A.

    The absorption spectra of UCl2-6 diluted into the cubic lattices Cs2ZrCl6 and Cs2SnCl6, and of UBr2-6 diluted into Cs2ZrBr6 have been measured at liquid helium temperatures. The derived energy levels, together with earlier luminescence measurements have been used to evaluate the crystal-field, spinorbit coupling, inter-electron repulsion and Trees correction parameters and the corresponding eigenvalues. Several of the states are derived from an almost equal admixture of two or more Russell-Saunders terms. Some magnetic properties are also computed and discussed.

  2. Faceting transitions in crystal growth and heteroepitaxial growth in the anisotropic phase-field crystal model

    NASA Astrophysics Data System (ADS)

    Chen, Cheng; Chen, Zheng; Zhang, Jing; Yang, Tao; Du, Xiu-Juan

    2012-11-01

    We modify the anisotropic phase-field crystal model (APFC), and present a semi-implicit spectral method to numerically solve the dynamic equation of the APFC model. The process results in the acceleration of computations by orders of magnitude relative to the conventional explicit finite-difference scheme, thereby, allowing us to work on a large system and for a long time. The faceting transitions introduced by the increasing anisotropy in crystal growth are then discussed. In particular, we investigate the morphological evolution in heteroepitaxial growth of our model. A new formation mechanism of misfit dislocations caused by vacancy trapping is found. The regular array of misfit dislocations produces a small-angle grain boundary under the right conditions, and it could significantly change the growth orientation of epitaxial layers.

  3. Phase-field-crystal methodology for modeling of structural transformations.

    PubMed

    Greenwood, Michael; Rottler, Jörg; Provatas, Nikolas

    2011-03-01

    We introduce and characterize free-energy functionals for modeling of solids with different crystallographic symmetries within the phase-field-crystal methodology. The excess free energy responsible for the emergence of periodic phases is inspired by classical density-functional theory, but uses only a minimal description for the modes of the direct correlation function to preserve computational efficiency. We provide a detailed prescription for controlling the crystal structure and introduce parameters for changing temperature and surface energies, so that phase transformations between body-centered-cubic (bcc), face-centered-cubic (fcc), hexagonal-close-packed (hcp), and simple-cubic (sc) lattices can be studied. To illustrate the versatility of our free-energy functional, we compute the phase diagram for fcc-bcc-liquid coexistence in the temperature-density plane. We also demonstrate that our model can be extended to include hcp symmetry by dynamically simulating hcp-liquid coexistence from a seeded crystal nucleus. We further quantify the dependence of the elastic constants on the model control parameters in two and three dimensions, showing how the degree of elastic anisotropy can be tuned from the shape of the direct correlation functions. PMID:21517507

  4. Subsurface Stress Fields in Single Crystal (Anisotropic) Contacts

    NASA Technical Reports Server (NTRS)

    Arakere, Nagaraj K.

    2003-01-01

    Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and fatigue stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent HCF failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and noncrystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. Techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts are presented in this report. Figure 1 shows typical damper contact locations in a turbine blade. The subsurface stress results are used for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades.

  5. Crystal Field Studies on MgGa2O4:Ni2+

    NASA Astrophysics Data System (ADS)

    Andreici, L.; Stanciu, M.; Avram, N. M.

    2010-08-01

    The energy levels scheme of octahedrally coordinated Ni2+ ion in single crystal, powder nano-single crystal, ceramics and glass-ceramics of MgGa2O4 host matrix, has been calculated in the exchange charge model of crystal field. The parameters of the crystal field acting on the Ni2+ ion are calculated from the crystal structure data, after optimization of the geometry of the system. The energy level schemes have been calculated by diagonalization of the crystal field Hamiltonian of this system. The obtained results were compared with experimental data; a good agreement were demonstrated, which confirm the validity of the model and used method.

  6. Modeling aligning effect of polymer network in polymer stabilized nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Yang, Deng-Ke; Cui, Yue; Nemati, Hossein; Zhou, Xiaochen; Moheghi, Alireza

    2013-12-01

    We developed a phenomenological theory to describe the aligning field of polymer networks in polymer stabilized liquid crystals where sub-micron size polymer networks are phase separated from the liquid crystal in dispersion. The polymer networks are anisotropic and anchor the liquid crystals in their longitudinal direction. They inhibit the liquid crystals reorientation when external stimuli, such as electric field and temperature, are applied and reduce the relaxation time from distorted states. We model the effects produced by the polymer networks as an effective aligning field. We calculate the effective field as a function of the polymer network volume fraction and the lateral size of the network. The theory is compared with experimental results and good agreements were obtained. It is very useful in predicting how much polymer networks change the driving voltage and response time of liquid crystal devices.

  7. Convection patterns and temperature fields of ammonothermal GaN bulk crystal growth process

    NASA Astrophysics Data System (ADS)

    Masuda, Yoshio; Sato, Osamu; Tomida, Daisuke; Yokoyama, Chiaki

    2016-05-01

    The natural convection heat transfer in an ammonothermal process for growing GaN bulk single crystals has been examined numerically. We consider only one crystal to simplify the calculation and discuss the relationship between convection patterns and temperature fields. Two types of convection patterns are observed owing to the difference in the crystal radius. When the convection pattern is transformed, the crystal surface temperature decreases as the crystal radius increases.

  8. Photorefractive effect at 775 nm in doped lithium niobate crystals

    SciTech Connect

    Nava, G.; Minzioni, P.; Cristiani, I.; Degiorgio, V.; Argiolas, N.; Bazzan, M.; Ciampolillo, M. V.; Pozza, G.; Sada, C.

    2013-07-15

    The photorefractive effect induced by 775-nm laser light on doped lithium niobate crystals is investigated by the direct observation in the far field of the transmitted-beam distortion as a function of time. Measurements performed at various Zr-doping concentrations and different light intensities show that the 775-nm light beam induces a steady-state photorefractive effect comparable to that of 532-nm light, but the observed build-up time of the photovoltaic field is longer by three-orders of magnitude. The 775-nm photorefractivity of lithium niobate crystals doped with 3 mol. % ZrO{sub 2} or with 5.5 mol. % MgO is found to be negligible.

  9. Cyano-substituted oligo(p-phenylene vinylene) single-crystal with balanced hole and electron injection and transport for ambipolar field-effect transistors.

    PubMed

    Deng, Jian; Tang, Jia; Xu, Yuanxiang; Liu, Liqun; Wang, Yan; Xie, Zengqi; Ma, Yuguang

    2015-02-01

    High and balanced hole and electron mobilities were achieved in OFETs based on the high photoluminescence of a 1,4-bis(2-cyano-2-phenylethenyl)benzene single-crystal with symmetric electrodes. For electron and hole, the operation voltage in the OFETs based on symmetric gold electrodes was 30 and -20 V, respectively. The accumulation threshold voltage is low enough for the OFETs to operate in an ambipolar model with the source/drain voltage (Vds) around 50 V despite the high injection barrier. The highest electron and hole mobility was 0.745 cm(2) V(-1) s(-1) and 0.239 cm(2) V(-1) s(-1), and the current density reached 90.7 and 27.4 A cm(-2), respectively with an assumed 10 nm accumulation layer. The high mobility comes from the strong π-π interactions. In addition, the highly ordered hydrogen bonding matrix may create an efficient route to pump the charge to the inner layer which can improve the injection ability. PMID:25530541

  10. Holographic effective field theories

    NASA Astrophysics Data System (ADS)

    Martucci, Luca; Zaffaroni, Alberto

    2016-06-01

    We derive the four-dimensional low-energy effective field theory governing the moduli space of strongly coupled superconformal quiver gauge theories associated with D3-branes at Calabi-Yau conical singularities in the holographic regime of validity. We use the dual supergravity description provided by warped resolved conical geometries with mobile D3-branes. Information on the baryonic directions of the moduli space is also obtained by using wrapped Euclidean D3-branes. We illustrate our general results by discussing in detail their application to the Klebanov-Witten model.

  11. Density change effects on crystal growth from the melt

    NASA Astrophysics Data System (ADS)

    Conti, Massimo

    2001-11-01

    When a crystal grows from its undercooled melt the local density changes, driving a convective flow in the liquid phase. Then, the purely diffusional description of the process ceases to be satisfactory. Moreover, the dynamic pressure associated with the flow field may affect the melting temperature (and the effective undercooling) of the system. Both these effects have been addressed in recent experimental work. In the present study we derive a thermodynamically consistent phase-field model that accounts for the density change effects in the solidification of a pure substance. Starting from a thermodynamic potential that includes squared gradient terms for both the order parameter and the density, the field equations are derived assuming positive local entropy production. The model is numerically solved in one dimension to show deviations from the classic phase-field description of the same phenomenon.

  12. Effect of 6H-SiC crystal growth shapes on thermo-elastic stress in the growing crystal

    NASA Astrophysics Data System (ADS)

    Shi, Yong-gui; Dai, Pei-yun; Yang, Jian-feng; Jin, Zhi-hao; Liu, Hu-lin

    2012-07-01

    The effect of 6H-SiC crystal growth shapes on the thermo-elastic stress distribution in the growing crystal was systematically investigated by using a finite element method. The thermo-elastic stress distribution in the crystal with a flat growth shape was more homogeneous than that in the crystals with concave and convex growth shapes, and the value of thermo-elasticity in the crystal with a flat growth shape was also smaller than that in the two other types of crystals. The maximum values of thermo-elastic stress appeared at interfaces between the crystal and the graphite lid. If the lid was of the same properties as 6H-SiC, the thermo-elastic stress would decrease in two orders of magnitude. Thus, to grow 6H-SiC single crystals of high quality, a transition layer of SiC formed by deposition or reaction is suggested; meanwhile the thermal field in the growth chamber should be adjusted to maintain the crystals with flat growth shapes.

  13. Accurate Full-Field Thermochromic Liquid Crystal Thermography for the Study of Instantaneous Turbulent Heat Transfer

    NASA Astrophysics Data System (ADS)

    Sabatino, D. R.; Praisner, T. J.; Smith, C. R.

    1998-11-01

    The color change of thermochromic liquid crystals with temperature can be effectively utilized as full-field surface temperature sensors to investigate the fundamental structure of wall turbulence. In order to accurately quantify turbulent heat transfer behavior, a new technique has been developed for the calibration of wide-band micro-encapsulated thermochromic liquid crystals. Lighting/viewing arrangements are described and evaluated for ease of implementation and accuracy of the displayed color. This new technique employs images recorded in-situ with the test surface systematically exposed to a series of uniform temperature conditions spanning the bandwidth of the liquid crystals. This sequence of images is used to generate point-wise color/temperature calibration curves for the entire surface. Experimental results will be presented illustrating the application of the technique for assessment of spatial/temporal surface heat transfer behavior due to selected turbulent flows in a water channel

  14. Electric Field-Induced Skyrmion Crystals via Charged Monopoles in Insulating Helimagets

    NASA Astrophysics Data System (ADS)

    Watanabe, Haruki; Vishwanath, Ashvin

    2016-06-01

    Electrons propagating in a magnetically ordered medium experience an additional gauge field associated with the Berry phase of their spin following the local magnetic texture. In contrast to the usual electromagnetic field, this gauge field admits monopole excitations, corresponding to hedgehog defects of the magnetic order. In an insulator, these hedgehogs carry a well-defined electric charge allowing for them to be controlled by electric fields. One particularly robust mechanism that contributes to the charge is the orbital magnetoelectric effect, captured by a θ angle, which leads to a charge of eθ/2π on hedgehogs. This is a direct consequence of the Witten effect for magnetic monopoles in a θ medium. A physical consequence is that external electric fields can induce skyrmion crystal phases in insulating helimagnets.

  15. Microwave field effect transistor

    NASA Technical Reports Server (NTRS)

    Huang, Ho-Chung (Inventor)

    1989-01-01

    Electrodes of a high power, microwave field effect transistor are substantially matched to external input and output networks. The field effect transistor includes a metal ground plane layer, a dielectric layer on the ground plane layer, a gallium arsenide active region on the dielectric layer, and substantially coplanar spaced source, gate, and drain electrodes having active segments covering the active region. The active segment of the gate electrode is located between edges of the active segments of the source and drain electrodes. The gate and drain electrodes include inactive pads remote from the active segments. The pads are connected directly to the input and output networks. The source electrode is connected to the ground plane layer. The space between the electrodes and the geometry of the electrodes extablish parasitic shunt capacitances and series inductances that provide substantial matches between the input network and the gate electrode and between the output network and the drain electrode. Many of the devices are connected in parallel and share a common active region, so that each pair of adjacent devices shares the same source electrodes and each pair of adjacent devices shares the same drain electrodes. The gate electrodes for the parallel devices are formed by a continuous stripe that extends between adjacent devices and is connected at different points to the common gate pad.

  16. Effect of dislocations on the acoustic properties of TGS crystals near the phase transition

    NASA Astrophysics Data System (ADS)

    Rakhimov, I.; Charnaia, E. V.; Shuvalov, L. A.; Shutilov, V. A.

    1985-09-01

    The effect of dislocations on the acoustic properties of triglycine sulfate (TGS) crystals is investigated experimentally near the phase transition during the imposition of a static external electric field. Results of the measurements of the temperature dependences of the sound velocity and of the ultrasonic absorption clearly show field-induced effects related to the presence of dislocations. The effect of dislocations on the acoustic properties of TGS is particularly pronounced in pure crystals containing a minimum number of point defects.

  17. Light scattering from liquid crystal director fluctuations in steady magnetic fields up to 25 tesla

    NASA Astrophysics Data System (ADS)

    Challa, Pavan K.; Curtiss, O.; Williams, J. C.; Twieg, R.; Toth, J.; McGill, S.; Jákli, A.; Gleeson, J. T.; Sprunt, S. N.

    2012-07-01

    We report on homodyne dynamic light scattering measurements of orientational fluctuation modes in both calamitic and bent-core nematic liquid crystals, carried out in the new split-helix resistive magnet at the National High Magnetic Field Laboratory. The relaxation rate and inverse scattered intensity of director fluctuations exhibit a linear dependence on field-squared up to 25 tesla, which is consistent with strictly lowest order coupling of the tensor order parameter Q to field (QαβBαBβ) in the nematic free energy. However, we also observe evidence of field dependence of certain nematic material parameters, an effect which may be expected from the mean field scaling of these quantities with the magnitude of Q and the predicted variation of Q with field.

  18. Light scattering from liquid crystal director fluctuations in steady magnetic fields up to 25 tesla.

    PubMed

    Challa, Pavan K; Curtiss, O; Williams, J C; Twieg, R; Toth, J; McGill, S; Jákli, A; Gleeson, J T; Sprunt, S N

    2012-07-01

    We report on homodyne dynamic light scattering measurements of orientational fluctuation modes in both calamitic and bent-core nematic liquid crystals, carried out in the new split-helix resistive magnet at the National High Magnetic Field Laboratory. The relaxation rate and inverse scattered intensity of director fluctuations exhibit a linear dependence on field-squared up to 25 tesla, which is consistent with strictly lowest order coupling of the tensor order parameter Q to field (Q(αβ)B(α)B(β)) in the nematic free energy. However, we also observe evidence of field dependence of certain nematic material parameters, an effect which may be expected from the mean field scaling of these quantities with the magnitude of Q and the predicted variation of Q with field. PMID:23005438

  19. Magnetic-field tunable multichannel filter in a plasma photonic crystal at microwave frequencies.

    PubMed

    Chang, Tsung-Wen; Chien, Jia-Ren Chang; Wu, Chien-Jang

    2016-02-01

    The microwave magnetic-field tunable filtering properties in a multichannel filter based on use of a one-dimensional finite magnetized plasma photonic crystal (PPC) are theoretically investigated. The considered PPC has a structure of air/(AB)N/air, where A is a dielectric layer, B is a plasma layer, and N is the stack number. First, in the absence of an externally applied magnetic field, the structure can work as a multichannel filter whose channel number is equal to N-1 for N>1. Next, in the presence of an externally applied field, the filtering properties become tunable, i.e., the channel frequencies can be shifted as a function of the applied magnetic field. We find that the effect of the magnetic field will cause the channel frequencies to be blue-shifted or red-shifted depending on the orientation of the applied magnetic field. PMID:26836104

  20. Fiber optic dynamic electric field sensor based on nematic liquid crystal Fabry-Perot etalon

    NASA Astrophysics Data System (ADS)

    Ko, Myeong Ock; Kim, Sung-Jo; Kim, Jong-Hyun; Jeon, Min Yong

    2014-05-01

    We propose a fiber-optic dynamic electric field sensor using a nematic liquid crystal (NLC) Fabry-Perot etalon and a wavelength-swept laser. The transmission wavelength of the NLC Fabry-Perot etalon depends on the applied electric field intensity. The change in the effective refractive index of the NLC is measured while changing the applied electric field intensity. It decreases from 1.67 to 1.51 as the applied the electric field intensity is increased. Additionally, we successfully measure the dynamic variation of the electric field using the high-speed wavelength-swept laser. By measuring the modulation frequency of the transmission peaks in the temporal domain, the frequency of the modulated electric field can be estimated.

  1. Magnonic Hall effect and topological magnonic crystals (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Murakami, Shuichi

    2015-09-01

    In electronic systems it is well established that when there is a magnetic field or spontaneous magnetization, the Hall effect, and in some cases the quantum Hall effect appears. We theoretically pursue analogs of these phenomena in magnons (spin waves) and plasmons. In the case of magnons in ferromagnets, the Hall effect or quantum Hall effect requires some kind of a spin-orbit coupling (similar to electronic systems), and we show that the dipolar interaction, as well as the Dyaloshinskii-Moriya interaction, plays the role. By calculating the Berry curvature from the wavefunction, we can calculate thermal Hall effect for magnons in ferromagnets with dipolar interaction. We found that only the magnetostatic forward volume-wave mode exhibits the thermal Hall effect while the backward mode and the surface mode do not. In addition, by introducing some artificial spatial periodicity into the magnet, for example by fabricating nanostructures with two different magnets in a periodic structure or by making a periodic array of nanomagnets, we theoretically find appearance of quantum Hall effect in a certain range of the magnetic field. There appear chiral edge states which propagate along the edge of the magnet in one way. We call this a topological magnonic crystal. In the plasmon case, we should begin with constructing a fundamental band theory, and we theoretically show that on a metal surface with corrugations forming a triangular lattice under the magnetic field, the quantum Hall effect appears. It can be called a topological plasmonic crystal.

  2. Angular effects on thermochromic liquid crystal thermography

    NASA Astrophysics Data System (ADS)

    Kodzwa, Paul M.; Eaton, John K.

    2007-12-01

    This paper directly discusses the effects of lighting and viewing angles on liquid crystal thermography. This is because although thermochromic liquid crystals (TLCs) are a widely-used and accepted tool in heat transfer research, little effort has been directed to analytically describing these effects. Such insight is invaluable for the development of effective mitigation strategies. Using analytical relationships that describe the perceived color shift, a systematic manner of improving the performance of a TLC system is presented. This is particularly relevant for applications where significant variations in lighting and/or viewing angles are expected (such as a highly curved surface). This discussion includes an examination of the importance of the definition of the hue angle used to calibrate the color of a TLC-painted surface. The theoretical basis of the validated high-accuracy calibration approach reported by Kodzwa et al. (Exp Fluids s00348-007-0310-6, 2007) is presented.

  3. Hyperspectral optical near-field imaging: Looking graded photonic crystals and photonic metamaterials in color

    NASA Astrophysics Data System (ADS)

    Dellinger, Jean; Van Do, K.; Le Roux, Xavier; de Fornel, Frédérique; Cassan, Eric; Cluzel, Benoît

    2012-10-01

    Using a scanning near-field optical microscope operating with a hyperspectral detection scheme, we report the direct observation of the mirage effect within an on-chip integrated artificial material made of a two dimensional graded photonic crystal. The light rainbow due to the material dispersion is quantified experimentally and quantitatively compared to three dimensional plane wave assisted Hamiltonian optics predictions of light propagation.

  4. Dislocation dynamics, plasticity and avalanche statistics using the phase-field crystal model

    NASA Astrophysics Data System (ADS)

    Angheluta, Luiza

    2013-03-01

    The plastic deformation of stressed crystalline materials is characterized by intermittency and scaling behavior. The sudden strain bursts arise from collective interactions between depinned crystal defects such as dislocations. Recent experiments on sheared nanocrystals provide insights into the connection between the crystal plasticity and the mean field theory of the depinning transition, based on the similar power-law statistics of avalanche events. However, a complete theoretical formulation of this connection is still lacking, as are high quality numerical data. Phase field crystal modelling provides an efficient numerical approach to simulating the dynamics of dislocations in plastic flows at finite temperature. Dislocations are naturally created as defects in a periodic ground state that is being sheared, without any ad hoc creation and annihilation rules. These crystal defects interact and annihilate with one another, generating a collective effect of avalanches in the global plastic strain rate. We examine the statistics of plastic avalanches both at finite and zero temperatures, and find good agreement with the predictions of the mean field interface depinning theory. Moreover, we predict universal scaling forms for the extreme statistics of avalanches and universal relations between the power-law exponents of avalanche duration, size and extreme value. These results account for the observed power-law distribution of the maximum amplitudes in acoustic emission experiments of crystal plasticity, but are also broadly applicable to other systems in the mean-field interface depinning universality class, ranging from magnets to earthquakes. The work reported here was performed in collaboration with: Georgios Tsekenis, Michael LeBlanc, Patrick Y Chan, Jon Dantzig, Karin Dahmen, and Nigel Goldenfeld. The work was supported by the Center for Physics of Geological Processes (Norway) through a post-doctoral grant, the National Science Foundation through grant NSF

  5. Electric field effect of relaxor ferroelectric (1 ‑ x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 crystals near morphotropic phase boundary composition probed by Brillouin scattering

    NASA Astrophysics Data System (ADS)

    Aftabuzzaman, Md; Kojima, Seiji

    2016-07-01

    The relaxor ferroelectric (1 ‑ x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (x = 0.30, PMN–30PT) single crystal was studied under the zero field and the externally applied dc electric field by using micro-Brillouin scattering and dielectric spectroscopies over a wide temperature range of 303–773 K. The noticeable thermal hysteresis of longitudinal acoustic (LA) shift (νB) was observed between zero field heating and zero field cooling processes. Under the electric field of 0.5 kV/cm along the [001] axis, the LA mode splitting was observed in νB due to the coexistence of ferroelectric macrodomain and nanodomain states caused by the random field, and in dielectric measurements the monoclinic (M) and tetragonal phases were appeared between rhombohedral and cubic phases. The LA mode splitting and M phase disappeared under the field of 1.0 kV/cm. The electric field dependence of LA velocity was studied at 304 K. The critical end point of the PMN–30PT single crystal was investigated.

  6. Effects of electric field on acoustic properties of 0.83Pb(Mg1/3Nb2/3) -0.17PbTiO3 single crystals studied by Brillouin light scattering

    NASA Astrophysics Data System (ADS)

    Kim, Tae Hyun; Ko, Jae-Hyeon; Kojima, Seiji

    2013-03-01

    Relaxor-based ferroelectric Pb[(Mg1/3Nb2/3)1-x Tix]O3 (PMN-xPT) single crystals have attracted great attention because of their exceptionally strong piezoelectric properties. This peculiar characteristic was attributed to the rotation of polarization directions and structural complexity. In this study, the phase transition behaviors of PMN-17PT single crystals have been investigated under an electric field applied along [001] by micro-Brillouin scattering. PMN-17PT single crystals were grown by the modified Bridgeman method. The two (001) surfaces were Au-coated to apply the electric field, and the coating was thin enough to allow the incident beam to transmit without much loss. The electric field of different values was applied to the sample along the [001] direction, and the Brillouin scattering spectrum was measured under both field-heating (FH) and field-cooling (FC) conditions. The electric field of 1kV/cm induced a new longitudinal acoustic (LA) mode component along with a broad Brillouin peak evolving continuously from the paraelectric phase during both FC and FH processes. This was attributed to the remnant polar nanoregions that were not aligned under the electric field due to quenched random fields. However, the splitting of the LA mode did not appear when the electric field was over 2kV/cm indicating a clear structural phase transition. This research was supported in part by the Marubun Research Promotion Foundation and Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0010497).

  7. Rheology of Pure Glasses and Crystal Bearing Melts: from the Newtonian Field to the Brittle Onset

    NASA Astrophysics Data System (ADS)

    Cordonnier, B.; Caricchi, L.; Pistone, M.; Castro, J. M.; Hess, K.; Dingwell, D. B.

    2010-12-01

    The brittle-ductile transition remains a central question of modern geology. If rocks can be perceived as a granular flow on geological time-scale, their behavior is brittle in dynamic areas. Understanding rock failure conditions is the main parameter in mitigating geological risks, more specifically the eruptive style transitions from effusive to explosive. If numerical simulations are the only way to fully understanding the physical processes involved, we are in a strong need of an experimental validation of the proposed models. here we present results obtained under torsion and uni-axial compression on both pure glasses and crystal bearing melts. We characterized the brittle onset of two phases magmas from 0 to 65% crystals. The strain-rates span a 5 orders magnitude range, from the Newtonian flow to the Brittle field (10-5 - 100 s-1). We particularly emphasize the time dependency of the measured rheology. The materials tested are a borosilicate glass from the National Bureau of Standards, a natural sample from Mt Unzen volcano and a synthetic sample. The lattest is an HPG8 melt with 7% sodium mole excess. The particles are quasi-isometric corundum crystalschosen for their shape and integrity under the stress range investigated. The crystal fraction ranges from 0 to 0.65. Concerning pure magmas, we recently demonstrated that the material passes from a Newtonian to a non-Nemtonian behavior with increasing strain-rate. This onset can mostly be explained by viscous-heating effects. However, for even greater strain-rates, the material cracks and finally fail. The brittle onset is here explained with the visco-elastic theory and corresponds to a Deborah number greater than 10-2. Concerning crystal bearing melts the departure from the Newtonian state is characterized by two effects: a shear-thinning and a time weakening effect. The first one is instantaneous and loading-unloading cyclic tests suggest an elastic contribution of the crystal network. The second one

  8. Peak effect phenomena, surface superconductivity and paramagnetic Meissner effect in a spherical single crystal of niobium

    NASA Astrophysics Data System (ADS)

    Das, Pradip; Tomy, C. V.; Takeya, H.; Ramakrishnan, S.; Grover, A. K.

    2009-03-01

    We have explored the vortex phase diagram in a spherical single crystal of niobium (Tc ~ 9.3 K) via isothermal and temperature dependent dc magnetization and ac-susceptibility measurements. The crystal has extremely weak pinning that can be inferred from the reversibility of M - H loops below Tc. However, one can visualize the peak effect (PE) feature in the isothermal M - H loops up to T = 8 K. The PE is also prominent in isothermal ac-susceptibility data for H > 750 Oe. An interesting observation in the present study is the prominent fingerprints of surface superconductivity, starting just above the collapse of pinning at the peak position of the PE and ending at the surface critical field (Hc3). We have also observed the paramagnetic Meissner effect in field-cooled magnetization data recorded at relatively large fields in this crystal. A vortex phase diagram is constructed by marking the peak positions of the PE (Hp), the upper critical field (Hc2) and the surface critical field (Hc3). Unlike a previous report which shows the existence of a multi-critical point in the phase diagram of a Nb crystal, where Hp, Hc2 and Hc3 lines meet, we do not observe a multi-critical point in our weak pinning crystal.

  9. Crystal-field levels in UBr 3 determined by neutron spectroscopy

    NASA Astrophysics Data System (ADS)

    Murasik, A.; Furrer, A.; Szczepaniak, W.

    1980-03-01

    Inelastic neutron scattering experiments have been performed in UBr 3 in order to determine the crystal-field levels. Four transitions between the ground state and all excited states have been observed, thus the crystal-field level scheme could be unambigously assigned. The Russell-Saunders coupling scheme has been used to derive the crystal-field parameters which cannot be accounted for by a simple point charge calculation.

  10. Inelastic neutron scattering investigation of crystal-field splittings in UBr 3

    NASA Astrophysics Data System (ADS)

    Murasik, A.; Furrer, A.

    1980-10-01

    An inelastic neutron scattering technique was used to measure the crystal-field splittings in UBr 3 at various temperatures and momentum transfers. In the interpretation of the observed energy spectra it turns out that the Russell-Saunders coupling scheme is a reasonable approximation. The crystal-field level scheme could be unambiguously assigned. The detailed nature of the crystal-field transition from the ground state to the first-excited state is not yet fully understood.

  11. Polymorphism, crystal nucleation and growth in the phase-field crystal model in 2D and 3D.

    PubMed

    Tóth, Gyula I; Tegze, György; Pusztai, Tamás; Tóth, Gergely; Gránásy, László

    2010-09-15

    We apply a simple dynamical density functional theory, the phase-field crystal (PFC) model of overdamped conservative dynamics, to address polymorphism, crystal nucleation, and crystal growth in the diffusion-controlled limit. We refine the phase diagram for 3D, and determine the line free energy in 2D and the height of the nucleation barrier in 2D and 3D for homogeneous and heterogeneous nucleation by solving the respective Euler-Lagrange (EL) equations. We demonstrate that, in the PFC model, the body-centered cubic (bcc), the face-centered cubic (fcc), and the hexagonal close-packed structures (hcp) compete, while the simple cubic structure is unstable, and that phase preference can be tuned by changing the model parameters: close to the critical point the bcc structure is stable, while far from the critical point the fcc prevails, with an hcp stability domain in between. We note that with increasing distance from the critical point the equilibrium shapes vary from the sphere to specific faceted shapes: rhombic dodecahedron (bcc), truncated octahedron (fcc), and hexagonal prism (hcp). Solving the equation of motion of the PFC model supplied with conserved noise, solidification starts with the nucleation of an amorphous precursor phase, into which the stable crystalline phase nucleates. The growth rate is found to be time dependent and anisotropic; this anisotropy depends on the driving force. We show that due to the diffusion-controlled growth mechanism, which is especially relevant for crystal aggregation in colloidal systems, dendritic growth structures evolve in large-scale isothermal single-component PFC simulations. An oscillatory effective pair potential resembling those for model glass formers has been evaluated from structural data of the amorphous phase obtained by instantaneous quenching. Finally, we present results for eutectic solidification in a binary PFC model. PMID:21386517

  12. Polymorphism, crystal nucleation and growth in the phase-field crystal model in 2D and 3D

    NASA Astrophysics Data System (ADS)

    Tóth, Gyula I.; Tegze, György; Pusztai, Tamás; Tóth, Gergely; Gránásy, László

    2010-09-01

    We apply a simple dynamical density functional theory, the phase-field crystal (PFC) model of overdamped conservative dynamics, to address polymorphism, crystal nucleation, and crystal growth in the diffusion-controlled limit. We refine the phase diagram for 3D, and determine the line free energy in 2D and the height of the nucleation barrier in 2D and 3D for homogeneous and heterogeneous nucleation by solving the respective Euler-Lagrange (EL) equations. We demonstrate that, in the PFC model, the body-centered cubic (bcc), the face-centered cubic (fcc), and the hexagonal close-packed structures (hcp) compete, while the simple cubic structure is unstable, and that phase preference can be tuned by changing the model parameters: close to the critical point the bcc structure is stable, while far from the critical point the fcc prevails, with an hcp stability domain in between. We note that with increasing distance from the critical point the equilibrium shapes vary from the sphere to specific faceted shapes: rhombic dodecahedron (bcc), truncated octahedron (fcc), and hexagonal prism (hcp). Solving the equation of motion of the PFC model supplied with conserved noise, solidification starts with the nucleation of an amorphous precursor phase, into which the stable crystalline phase nucleates. The growth rate is found to be time dependent and anisotropic; this anisotropy depends on the driving force. We show that due to the diffusion-controlled growth mechanism, which is especially relevant for crystal aggregation in colloidal systems, dendritic growth structures evolve in large-scale isothermal single-component PFC simulations. An oscillatory effective pair potential resembling those for model glass formers has been evaluated from structural data of the amorphous phase obtained by instantaneous quenching. Finally, we present results for eutectic solidification in a binary PFC model.

  13. Study of Effects of Gravity on Crystallization

    NASA Technical Reports Server (NTRS)

    Smith, Guy A.; Workman, Gary L.; OBrian, Susan

    1996-01-01

    The effect of gravity on the crystallization behavior of fluoride fibers is being investigated by performing fiber annealing experiments on NASA's KC-135 using commercial grade fibers donated by industrial partners. The successful observations of reduced formation of microcrystallites in reduced gravity of the parabolic flights will be repeated to confirm earlier results. The design and implementation of an automated sting assembly for use in space fiber drawing experiments will also be emphasized in this study.

  14. High-resolution X-ray absorption spectroscopy as a probe of crystal-field and covalency effects in actinide compounds.

    PubMed

    Butorin, Sergei M; Kvashnina, Kristina O; Vegelius, Johan R; Meyer, Daniel; Shuh, David K

    2016-07-19

    Applying the high-energy resolution fluorescence-detection (HERFD) mode of X-ray absorption spectroscopy (XAS), we were able to probe, for the first time to our knowledge, the crystalline electric field (CEF) splittings of the [Formula: see text] shell directly in the HERFD-XAS spectra of actinides. Using ThO2 as an example, data measured at the Th 3d edge were interpreted within the framework of the Anderson impurity model. Because the charge-transfer satellites were also resolved in the HERFD-XAS spectra, the analysis of these satellites revealed that ThO2 is not an ionic compound as previously believed. The Th [Formula: see text] occupancy in the ground state was estimated to be twice that of the Th [Formula: see text] states. We demonstrate that HERFD-XAS allows for characterization of the CEF interaction and degree of covalency in the ground state of actinide compounds as it is extensively done for 3d transition metal systems. PMID:27370799

  15. Spectral and polarization structure of field-induced photonic bands in cholesteric liquid crystals

    NASA Astrophysics Data System (ADS)

    Palto, S. P.; Barnik, M. I.; Geivandov, A. R.; Kasyanova, I. V.; Palto, V. S.

    2015-09-01

    Transmission of planar layers of cholesteric liquid crystals is studied in pulsed electric fields perpendicular to the helix axis at normal incidence of both linearly polarized and unpolarized light. Spectral and light polarization properties of the primary photonic band and the field-induced bands up to fourth order of Bragg selective reflection are studied in detail. In our experiments we have achieved an electric field strength several times higher than the theoretical values corresponding to the critical field of full helix unwinding. However, the experiments show that despite the high strength of the electric field applied the helix does not unwind, but strongly deforms, keeping its initial spatial period. Strong helix deformation results in distinct spectral band splitting, as well as very high field-induced selective reflectance that can be applied in lasers and other optoelectronic devices. Peculiarities of inducing and splitting the bands are discussed in terms of the scattering coefficient approach. All observed effects are confirmed by numerical simulations. The simulations also show that liquid crystal surface anchoring is not the factor that prevents the helix unwinding. Thus, the currently acknowledged concept of continuous helix unwinding in the electric field should be reconsidered.

  16. Imprint electric field controlled electronic transport in TlGaSe2 crystals

    NASA Astrophysics Data System (ADS)

    Seyidov, MirHasan Yu; Suleymanov, Rauf A.; Balaban, Ertan; Şale, Yasin

    2013-09-01

    The effect of built-in electric field onto the dc electrical conductivity, photoconductivity, and electrical switching phenomenon were investigated in TlGaSe2 layered semiconductor within the temperature range of 77-300 K. We have used different types of electrodes for different TlGaSe2 samples in both parallel and perpendicular directions to the plane of layers. The effect of electric field was investigated by cooling the samples from the room temperature under the electric field and then removing it at ˜80 K. After the procedure, it was found that a built-in internal electric field which strongly affects transport properties appears in TlGaSe2 crystals. Substantial increasing of both dark currents and photo-conductivities were observed predominantly at low temperatures, where hopping was the main conductivity mechanism. The anomalous decrease of the activation energy in the low temperature region and the switching effect are also the main experimental findings of the present work. Such behavior can be understood by assuming that the built-in electric field greatly increases the contribution of the hopping conductivity at low temperatures. Obtained results are discussed on the basis of the models widely used for disordered semiconductors. It was shown that TlGaSe2 crystal demonstrates the peculiar behavior that is typical to such type of semiconductors.

  17. Optical electric-field sensor based on angular optical bias using single β-BaB2O4 crystal.

    PubMed

    Li, Changsheng; Shen, Xiaoli; Zeng, Rong

    2013-11-01

    A novel optical electric-field sensor is proposed and demonstrated in experiment by use of a single beta barium borate (β-BaB2O4, BBO) crystal. The optical sensing unit is only composed of one BBO crystal and two polarizers. An optical phase bias of 0.5π is provided by using natural birefringence in the BBO crystal itself. A small angle (e.g., 0.6°) between the sensing light beam and principal axis of the crystal is required in order to produce the above optical bias. Thus the BBO crystal is used as the electric-field-sensing element and quarter waveplate. The ac electric field in the range of (1.4-703.2) kV/m has been measured with measurement sensitivity of 1.39 mV/(kV/m) and nonlinear error of 0.6%. Compared with lithium niobate crystal used as an electric-field sensor, main advantages of the BBO crystal include higher measurement sensitivity, compact configuration, and no ferroelectric ringing effect. PMID:24216661

  18. Phase field crystal study of nano-crack growth and branch in materials

    NASA Astrophysics Data System (ADS)

    Yingjun, Gao; Zhirong, Luo; Lilin, Huang; Hong, Mao; Chuanggao, Huang; Kui, Lin

    2016-06-01

    The phase field crystal (PFC) method is a new multiscale method, which can reproduce physical phenomena on an atomic level and on a diffusion time scale for the microstructure evolution of materials. The morphology of microcrack propagation and the branch of single crystal materials under tensile strain with a fixed grip condition are simulated by using PFC coupling with an external field method. The results show that microcrack propagation depends a lot on the applied strain. The crack starts to grow and branch when the strain reaches a critical value for biaxial tension. The temperature parameter may also have an effect on crack propagation and the branch. In order to indicate the connection between the PFC results and materials behavior, the energy balance approach is used to analyze the mechanism of crack extension, and also the critical value of the strain for crack extension is obtained. The simulated results are in good agreement with other simulation results and experimental results.

  19. Glassy phases and driven response of the phase-field-crystal model with random pinning.

    PubMed

    Granato, E; Ramos, J A P; Achim, C V; Lehikoinen, J; Ying, S C; Ala-Nissila, T; Elder, K R

    2011-09-01

    We study the structural correlations and the nonlinear response to a driving force of a two-dimensional phase-field-crystal model with random pinning. The model provides an effective continuous description of lattice systems in the presence of disordered external pinning centers, allowing for both elastic and plastic deformations. We find that the phase-field crystal with disorder assumes an amorphous glassy ground state, with only short-ranged positional and orientational correlations, even in the limit of weak disorder. Under increasing driving force, the pinned amorphous-glass phase evolves into a moving plastic-flow phase and then, finally, a moving smectic phase. The transverse response of the moving smectic phase shows a vanishing transverse critical force for increasing system sizes. PMID:22060323

  20. Interfacial free energy adjustable phase field crystal model for homogeneous nucleation.

    PubMed

    Guo, Can; Wang, Jincheng; Wang, Zhijun; Li, Junjie; Guo, Yaolin; Huang, Yunhao

    2016-05-18

    To describe the homogeneous nucleation process, an interfacial free energy adjustable phase-field crystal model (IPFC) was proposed by reconstructing the energy functional of the original phase field crystal (PFC) methodology. Compared with the original PFC model, the additional interface term in the IPFC model effectively can adjust the magnitude of the interfacial free energy, but does not affect the equilibrium phase diagram and the interfacial energy anisotropy. The IPFC model overcame the limitation that the interfacial free energy of the original PFC model is much less than the theoretical results. Using the IPFC model, we investigated some basic issues in homogeneous nucleation. From the viewpoint of simulation, we proceeded with an in situ observation of the process of cluster fluctuation and obtained quite similar snapshots to colloidal crystallization experiments. We also counted the size distribution of crystal-like clusters and the nucleation rate. Our simulations show that the size distribution is independent of the evolution time, and the nucleation rate remains constant after a period of relaxation, which are consistent with experimental observations. The linear relation between logarithmic nucleation rate and reciprocal driving force also conforms to the steady state nucleation theory. PMID:27117814

  1. Faraday isolator based on a TSAG single crystal with compensation of thermally induced depolarization inside magnetic field

    NASA Astrophysics Data System (ADS)

    Snetkov, Ilya; Palashov, Oleg

    2015-04-01

    A Faraday isolator based on a terbium scandium aluminum garnet (TSAG) single crystal with compensation of thermally induced depolarization inside magnetic field was demonstrated. An isolation ratio of 32 dB at 350 W cw laser radiation power was achieved. Thermally induced depolarization and thermal lens were studied and compared with similar thermal effects arising in the widely used terbium gallium garnet crystal (TGG) for the first time.

  2. Change in the microhardness of nonmagnetic crystals after their exposure to the Earth's magnetic field and AC pump field in the EPR scheme

    NASA Astrophysics Data System (ADS)

    Alshits, V. I.; Darinskaya, E. V.; Koldaeva, M. V.; Petrzhik, E. A.

    2012-02-01

    Changes in the microhardness of ZnO, triglycine sulfate (TGS), and potassium acid phthalate (KAP) crystals after their exposure to crossed ultralow magnetic fields, i.e., the Earth's field B Earth ≈ 50 μT and the alternating-current field tilde B ≈ 3 μ T orthogonal to it, have been revealed. In ZnO crystals, the microhardness increases, whereas in TGS and KAP, it decreases. A maximum change (10-15%) is reached within 1-3 h after magnetic treatment; then, the microhardness gradually recovers to its initial value for the first day. After a sufficient pause, the effect is completely reproduced under the same conditions. The resonant frequency of the pump field tilde B corresponds to the EPR condition with a g-factor close to two. The magnetic memory exhibits a strong anisotropy: for each of the crystals, a direction is found, which, being coincident with the Earth's magnetic field vector B Earth, causes complete or partial suppression of the effect. In ZnO and TGS crystals, these are symmetry axes 6 and 2, respectively. In the KAP crystal, it is the direction in the cleavage plane orthogonal the 2 axis. Possible physical mechanisms of the observed phenomena have been discussed.

  3. Electric-field-assisted position and orientation control of organic single crystals.

    PubMed

    Kotsuki, Kenji; Obata, Seiji; Saiki, Koichiro

    2014-12-01

    We have investigated the motion of growing pentacene single crystals in solution under various electric fields. The pentacene single crystals in 1,2,4-trichlorobenzene responded to the electric field as if they were positively charged. By optimizing the strength and frequency of an alternating electric field, the pentacene crystals automatically bridged the electrodes on SiO2. The pentacene crystal with a large aspect ratio tended to direct the [1̅10] orientation parallel to the conduction direction, which will be suitable from a viewpoint of anisotropy in mobility. The present result shows a possibility of controlling the position and orientation of organic single crystals by the use of an electric field, which leads to high throughput and low cost industrial manufacturing of the single crystal array from solution. PMID:25360544

  4. Fabrication of Crystals and Devices for Studies of Field Induced Superconductivity

    NASA Astrophysics Data System (ADS)

    Kloc, Christian

    2002-03-01

    It was demonstrated that injection of electrons or holes into materials using field effect transistor can transform the surface layer into a metal or at low enough temperatures even into a superconductor. Which substances could exhibit electric field induced superconductivity is currently not well know. Superconductivity has been successfully induced in single crystals of arenes, (pentacene Tc = 2 K, tetracene Tc = 2.7K, anthracene Tc = 4 K) oligophenylenevinylenes (trimer Tc =4.2K , tetramer Tc=2.9 K and pentamer, Tc= 2 K) sexithiophene, polymer thin film (regioregular polythiophene, Tc = 2.35 K) and single crystals of pure and intercalated fullerenes (hole and electron doped C60 Tc = 52 and 11K, C70, Tc = 7K and substituted C60, Tc = up to 117 K). Additional, Schon et al. have reported the observation of field induced superconductivity in copper oxide compounds. Despite of relative simple device structures, they consist of semiconducting single crystals or well oriented thin films, metal source and drain electrodes, an aluminum oxide dielectric layer and a conducting gate electrode, the fabrication is onerous and the significance of particular technological steps to functionality of a whole device is not well explored. In this presentation I would like to discuss these technological procedures leading to superconducting devices and further developments in search for high temperature superconducting organics.

  5. Determination of forced convection parameters by interferometric imaging of the concentration field during growth of KDP crystals

    NASA Astrophysics Data System (ADS)

    Verma, Sunil; Muralidhar, K.

    2011-07-01

    Growth of a potassium dihydrogen phosphate (KDP) crystal from its aqueous solution has been considered under forced convection conditions. The KDP crystal is grown in a conventional top hanging geometry. Forced convection conditions are created by rotating the crystal about a vertical axis. The rotational RPM is varied in a cycle, creating an accelerated rotation (AR) paradigm. The effect of varying the rotational RPM on the concentration field around the crystal was investigated. Mach-Zehnder interferometry was adopted as an optical technique to image the evolving concentration fields. Six different experiments were performed to obtain the specific set of time periods and rotation rates of the acceleration cycle that result in a uniform concentration field around the growing crystal. The Reynolds number, an index of the strength of forced convection, was optimized through the experiments. The optimized parameters of the accelerated rotation cycle were found to be as follows: maximum rotation rate of 32 RPM, spin up period=40 s, spin down period=40 s, steady period=40 s, and stationary period=40 s. The parametric study further revealed that concentration was highly sensitive to the maximum rotation rate adopted during the AR cycle. It did not depend crucially on the time periods that could be varied by as much as ±25% around the respective average values. Finally, a KDP crystal was grown using the optimized forced convection parameters and the crystal quality was found to be good.

  6. A three-dimensional phase field model coupled with lattice kinetics solver for modeling crystal growth in furnaces with accelerated crucible rotation and traveling magnetic field

    SciTech Connect

    Lin, Guang; Bao, Jie; Xu, Zhijie

    2014-11-01

    In this study, which builds on other related work, we present a new three-dimensional numerical model for crystal growth in a vertical solidification system. This model accounts for buoyancy, accelerated crucible rotation technique (ACRT), and traveling magnetic field (TMF) induced convective flow and their effect on crystal growth and the chemical component's transport process. The evolution of the crystal growth interface is simulated using the phase field method. A semi-implicit lattice kinetics solver based on the Boltzmann equation is employed to model the unsteady incompressible flow. A one-way coupled concentration transport model is used to simulate the component fraction variation in both the liquid and solid phases, which can be used to check the quality of the crystal growth.

  7. Superconducting Field-Effect Transistors

    NASA Technical Reports Server (NTRS)

    Bhasin, Kul; Romanofsky, Robert R.; Tabib-Azar, Massood

    1995-01-01

    Devices offer switching speeds greater than semiconducting counterparts. High-Tc superconducting field-effect transistors (SUPEFETs) investigated for use as electronic switches in delay-line-type microwave phase shifters. Resemble semiconductor field-effect transistors in some respects, but their operation based on different principle; namely, electric-field control of transition between superconductivity and normal conductivity.

  8. Crystal-field calculations for transition-metal ions by application of an opposing potential

    DOE PAGESBeta

    Zhou, Fei; Aberg, Daniel

    2016-02-16

    We propose a fully ab initio method, the opposing crystal potential (OCP), to calculate the crystal-field parameters of transition-metal impurities in insulator hosts. Through constrained density functional calculations, OCP obtains the constraining Lagrange multipliers, which act as a cancellation potential against the crystal field and lead to spherical d-electron distribution. Furthermore, the method is applied to several insulators doped with Mn4+ and Mn2+ ions and shown to be in good agreement with experiment.

  9. Synthesis and superconducting properties of FeTe1-xSe Single Crystals under high magnetic fields

    NASA Astrophysics Data System (ADS)

    Gebre, Tesfaye; Li, G.; Whalen, J.; Conner, B.; Kostov, M.; Siegrist, T.; Balicas, L.

    2011-03-01

    Single crystals of superconductor FeTe 1-x Se x (0.1 <= x <= 0.5) were synthesized using optical floating zone, Bridgeman technique, and solid stat reaction. The samples were synthesized under various temperature gradients and cooling rates. Crystals were characterized via EDX, X-ray scattering, magnetization and transport measurements. Upper critical fields Hc 2 as estimated through the Werthamer-Hohenberg-Helfand (WHH) formalism indicate that these materials strongly surpass the weak coupling Pauli limiting field indicating that the shape of their phase diagram under field is essentially controlled by the Pauli effect. Annealing, leads to a metallic temperature dependence of the resistivity, and to sharper superconducting transitions. Despite the relatively small increase in single crystallinity, as quantified by single crystal x-ray diffraction measurements, we observe a different phase diagram under high magnetic fields when compared to non-annealed samples.

  10. Tunable Lamb wave band gaps in two-dimensional magnetoelastic phononic crystal slabs by an applied external magnetostatic field.

    PubMed

    Zhou, Changjiang; Sai, Yi; Chen, Jiujiu

    2016-09-01

    This paper theoretically investigates the band gaps of Lamb mode waves in two-dimensional magnetoelastic phononic crystal slabs by an applied external magnetostatic field. With the assumption of uniformly oriented magnetization, an equivalent piezomagnetic material model is used. The effects of magnetostatic field on phononic crystals are considered carefully in this model. The numerical results indicate that the width of the first band gap is significantly changed by applying the external magnetic field with different amplitude, and the ratio between the maximum and minimum gap widths reaches 228%. Further calculations demonstrate that the orientation of the magnetic field obviously affects the width and location of the first band gap. The contactless tunability of the proposed phononic crystal slabs shows many potential applications of vibration isolation in engineering. PMID:27281285