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MIT Open Access Articles

Mostrando recursos 1 - 20 de 26.043

  1. UV-solvent annealing for morphology and orientation control in self-assembled PS-PDMS thin films

    Ntetsikas, K; Liontos, G; Avgeropoulos, A; Lee, Keehong; Kreider, Melissa E.; Bai, Wubin; Cheng, Li-Chen; Dinachali, Saman Safari; Tu, Kun-Hua; Huang, Tao; Ross, Caroline A
    The response of polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS) thin films to UV exposure during solvent vapor annealing is described, in order to improve their applicability in nanolithography and nanofabrication. Two BCPs were examined, one with the PS block as majority (f[subscript PS] = 68%, M[subscript n] = 53 kg mol⁻¹), the other with PDMS block as majority (f[subscript PDMS] = 67%, M[subscript n] = 44 kg mol⁻¹). A 5 min UV irradiation was applied during solvent vapor annealing which led to both partial crosslinking of the polymer and a small increase in the temperature of the annealing chamber. This approach was effective for...

  2. Interface electronic structure at the topological insulator–ferrimagnetic insulator junction

    Kubota, Y; Murata, K; Miyawaki, J; Ozawa, K; Shirasawa, T; Feng, B; Yamamoto, Sh; Liu, R-Y; Yamamoto, S; Mahatha, S K; Sheverdyaeva, P; Moras, P; Suga, S; Harada, Y; Wang, K L; Matsuda, I; Onbasli, Mehmet Cengiz; Ross, Caroline A
    An interface electron state at the junction between a three-dimensional topological insulator film, Bi₂Se₃, and a ferrimagnetic insulator film, Y₃Fe₅O₁₂ (YIG), was investigated by measurements of angle-resolved photoelectron spectroscopy and x-ray absorption magnetic circular dichroism. The surface state of the Bi₂Se₃ film was directly observed and localized 3d spin states of the Fe ³⁺ in the YIG film were confirmed. The proximity effect is likely described in terms of the exchange interaction between the localized Fe 3d electrons in the YIG film and delocalized electrons of the surface and bulk states in the Bi₂Se₃ film.

  3. Temporal Evolution of Auto-Oscillations in an Yttrium-Iron-Garnet/Platinum Microdisk Driven by Pulsed Spin Hall Effect-Induced Spin-Transfer Torque

    Lauer, Viktor; Schneider, Michael; Meyer, Thomas; Bracher, Thomas; Pirro, Philipp; Heinz, Bjorn; Heussner, Frank; Lagel, Bert; Hillebrands, Burkard; Chumak, Andrii V.; Onbasli, Mehmet Cengiz; Ross, Caroline A
    The temporal evolution of pulsed spin Hall effect-spin transfer torque (SHE-STT) driven auto-oscillations in a yttrium iron garnet (YIG)-platinum (Pt) microdisk is studied experimentally using time-resolved Brillouin light scattering spectroscopy. The frequency of the auto-oscillations is different in the center when compared to the edge of the disk and is related to the simultaneous STT excitation of a bullet and a non-localized spin-wave mode. Furthermore, the magnetization precession intensity saturates on a time scale of 20 ns or longer, depending on the current density. For this reason, our findings suggest that a proper ratio between the current and the pulse...

  4. Control and local measurement of the spin chemical potential in a magnetic insulator

    Du, Chunhui; van der Sar, Toeno; Zhou, Tony X.; Upadhyaya, Pramey; Casola, Francesco; Zhang, Huiliang; Walsworth, Ronald L.; Tserkovnyak, Yaroslav; Yacoby, Amir; Onbasli, Mehmet Cengiz; Ross, Caroline A
    The spin chemical potential characterizes the tendency of spins to diffuse. Probing this quantity could provide insight into materials such as magnetic insulators and spin liquids and aid optimization of spintronic devices. Here we introduce single-spin magnetometry as a generic platform for nonperturbative, nanoscale characterization of spin chemical potentials. We experimentally realize this platform using diamond nitrogen-vacancy centers and use it to investigate magnons in a magnetic insulator, finding that the magnon chemical potential can be controlled by driving the system’s ferromagnetic resonance. We introduce a symmetry-based two-fluid theory describing the underlying magnon processes, measure the local thermomagnonic torque, and...

  5. The role of Snell’s law for a magnonic majority gate

    Kanazawa, Naoki; Goto, Taichi; Sekiguchi, Koji; Granovsky, Alexander B.; Takagi, Hiroyuki; Nakamura, Yuichi; Uchida, Hironaga; Inoue, Mitsuteru; Ross, Caroline A
    In the fifty years since the postulation of Moore's Law, the increasing energy consumption in silicon electronics has motivated research into emerging devices. An attractive research direction is processing information via the phase of spin waves within magnonic-logic circuits, which function without charge transport and the accompanying heat generation. The functional completeness of magnonic logic circuits based on the majority function was recently proved. However, the performance of such logic circuits was rather poor due to the difficulty of controlling spin waves in the input junction of the waveguides. Here, we show how Snell's law describes the propagation of spin...

  6. Origins of bad-metal conductivity and the insulator–metal transition in the rare-earth nickelates

    Ha, Sieu D.; Silevitch, D. M.; Ramanathan, Shriram; Jaramillo, Rafael
    For most metals, increasing temperature (T) or disorder hastens electron scattering. The electronic conductivity (σ) decreases as T rises because electrons are more rapidly scattered by lattice vibrations. The value of σ decreases as disorder increases because electrons are more rapidly scattered by imperfections in the material. This is the scattering rate hypothesis, which has guided our understanding of metal conductivity for over a century. However, for so-called bad metals with very low σ this hypothesis predicts scattering rates so high as to conflict with Heisenberga's uncertainty principle. Bad-metal conductivity has remained a puzzle since its initial discovery in the...

  7. Origins of bad-metal conductivity and the insulator–metal transition in the rare-earth nickelates

    Ha, Sieu D.; Silevitch, D. M.; Ramanathan, Shriram; Jaramillo, Rafael
    For most metals, increasing temperature (T) or disorder hastens electron scattering. The electronic conductivity (σ) decreases as T rises because electrons are more rapidly scattered by lattice vibrations. The value of σ decreases as disorder increases because electrons are more rapidly scattered by imperfections in the material. This is the scattering rate hypothesis, which has guided our understanding of metal conductivity for over a century. However, for so-called bad metals with very low σ this hypothesis predicts scattering rates so high as to conflict with Heisenberga's uncertainty principle. Bad-metal conductivity has remained a puzzle since its initial discovery in the...

  8. Solid-state graft copolymer electrolytes for lithium battery applications

    Hu, Qichao; Caputo, Antonio; Sadoway, Donald Robert
    Battery safety has been a very important research area over the past decade. Commercially available lithium ion batteries employ low flash point ( < 80 °C), flammable, and volatile organic electrolytes. These organic based electrolyte systems are viable at ambient temperatures, but require a cooling system to ensure that temperatures do not exceed 80 °C. These cooling systems tend to increase battery costs and can malfunction which can lead to battery malfunction and explosions, thus endangering human life. Increases in petroleum prices lead to a huge demand for safe, electric hybrid vehicles that are more economically viable to operate as...

  9. Solid-state graft copolymer electrolytes for lithium battery applications

    Hu, Qichao; Caputo, Antonio; Sadoway, Donald Robert
    Battery safety has been a very important research area over the past decade. Commercially available lithium ion batteries employ low flash point ( < 80 °C), flammable, and volatile organic electrolytes. These organic based electrolyte systems are viable at ambient temperatures, but require a cooling system to ensure that temperatures do not exceed 80 °C. These cooling systems tend to increase battery costs and can malfunction which can lead to battery malfunction and explosions, thus endangering human life. Increases in petroleum prices lead to a huge demand for safe, electric hybrid vehicles that are more economically viable to operate as...

  10. Angle-selective perfect absorption with two-dimensional materials

    Zhu, Linxiao; Liu, Fengyuan; Yu, Zongfu; Wang, Xinran; Fan, Shanhui; Lin, Hongtao; Hu, Juejun
    Two-dimensional (2D) materials have great potential in photonic and optoelectronic devices. However, the relatively weak light absorption in 2D materials hinders their application in practical devices. Here, we propose a general approach to achieve angle-selective perfect light absorption in 2D materials. As a demonstration of the concept, we experimentally show giant light absorption by placing large-area single-layer graphene on a structure consisting of a chalcogenide layer atop a mirror and achieving a total absorption of 77.6% in the mid-infrared wavelength range (~13 μm), where the graphene contributes a record-high 47.2% absorptivity of mid-infrared light. Construction of such an angle-selective thin optical...

  11. Angle-selective perfect absorption with two-dimensional materials

    Zhu, Linxiao; Liu, Fengyuan; Yu, Zongfu; Wang, Xinran; Fan, Shanhui; Lin, Hongtao; Hu, Juejun
    Two-dimensional (2D) materials have great potential in photonic and optoelectronic devices. However, the relatively weak light absorption in 2D materials hinders their application in practical devices. Here, we propose a general approach to achieve angle-selective perfect light absorption in 2D materials. As a demonstration of the concept, we experimentally show giant light absorption by placing large-area single-layer graphene on a structure consisting of a chalcogenide layer atop a mirror and achieving a total absorption of 77.6% in the mid-infrared wavelength range (~13 μm), where the graphene contributes a record-high 47.2% absorptivity of mid-infrared light. Construction of such an angle-selective thin optical...

  12. On-chip chalcogenide glass waveguide-integrated mid-infrared PbTe detectors

    Li, J.; Huang, X.; Richardson, K.; Tan, D. T. H.; Han, Zhaohong; Singh, Vijay Raj; Kita, Derek M.; Monmeyran, Corentin Pierre; Becla, Piotr; Su, Peter; Kimerling, Lionel C; Hu, J.; Agarwal, Anuradha
    We experimentally demonstrate an on-chip polycrystalline PbTe photoconductive detector integrated with a chalcogenide glass waveguide. The device is monolithically fabricated on silicon, operates at room-temperature, and exhibits a responsivity of 1.0 A/W at wavelengths between 2.1 and 2.5 μm.

  13. On-chip chalcogenide glass waveguide-integrated mid-infrared PbTe detectors

    Li, J.; Huang, X.; Richardson, K.; Tan, D. T. H.; Han, Zhaohong; Singh, Vijay Raj; Kita, Derek M.; Monmeyran, Corentin Pierre; Becla, Piotr; Su, Peter; Kimerling, Lionel C; Hu, J.; Agarwal, Anuradha
    We experimentally demonstrate an on-chip polycrystalline PbTe photoconductive detector integrated with a chalcogenide glass waveguide. The device is monolithically fabricated on silicon, operates at room-temperature, and exhibits a responsivity of 1.0 A/W at wavelengths between 2.1 and 2.5 μm.

  14. Integrated photonics for infrared spectroscopic sensing

    Yadav, Anupama; Richardson, Kathleen; Lin, Hongtao; Kita, Derek M.; Han, Zhaohong; Su, Peter; Agarwal, Anuradha; Gu, Tian; Hu, Juejun
    Infrared (IR) spectroscopy is widely recognized as a gold standard technique for chemical analysis. Traditional IR spectroscopy relies on fragile bench-Top instruments located in dedicated laboratory settings, and is thus not suitable for emerging field-deployed applications such as in-line industrial process control, environmental monitoring, and point-ofcare diagnosis. Recent strides in photonic integration technologies provide a promising route towards enabling miniaturized, rugged platforms for IR spectroscopic analysis. Chalcogenide glasses, the amorphous compounds containing S, Se or Te, have stand out as a promising material for infrared photonic integration given their broadband infrared transparency and compatibility with silicon photonic integration. In this...

  15. Integrated photonics for infrared spectroscopic sensing

    Yadav, Anupama; Richardson, Kathleen; Lin, Hongtao; Kita, Derek M.; Han, Zhaohong; Su, Peter; Agarwal, Anuradha; Gu, Tian; Hu, Juejun
    Infrared (IR) spectroscopy is widely recognized as a gold standard technique for chemical analysis. Traditional IR spectroscopy relies on fragile bench-Top instruments located in dedicated laboratory settings, and is thus not suitable for emerging field-deployed applications such as in-line industrial process control, environmental monitoring, and point-ofcare diagnosis. Recent strides in photonic integration technologies provide a promising route towards enabling miniaturized, rugged platforms for IR spectroscopic analysis. Chalcogenide glasses, the amorphous compounds containing S, Se or Te, have stand out as a promising material for infrared photonic integration given their broadband infrared transparency and compatibility with silicon photonic integration. In this...

  16. The role of ceramic and glass science research in meeting societal challenges: Report from an NSF-sponsored workshop

    Faber, Katherine T.; Asefa, Tewodros; Backhaus-Ricoult, Monika; Brow, Richard; Chan, Julia Y.; Dillon, Shen; Fahrenholtz, William G.; Finnis, Michael W.; Garay, Javier E.; García, R. Edwin; Gogotsi, Yury; Haile, Sossina M.; Halloran, John; Huang, Liping; Jacobsen, Steven D.; Lara-Curzio, Edgar; LeBeau, James; Lee, William E.; Levi, Carlos G.; Levin, Igor; Lewis, Jennifer A.; Lipkin, Don M.; Lu, Kathy; Luo, Jian; Maria, Jon-Paul; Martin, Lane W.; Martin, Steve; Messing, Gary; Navrotsky, Alexandra; Padture, Nitin P.; Randall, Clive; Rohrer, Gregory S.; Rosenflanz, Anatoly; Schaedler, Tobias A.; Schlom, Darrell G.; Sehirlioglu, Alp; Stevenson, Adam J.; Tani, Toshihiko; Tikare, Veena; Trolier-McKinstry, Susan; Wang, Hong; Hu, Juejun; Yildiz, Bilge
    Under the sponsorship of the U.S. National Science Foundation, a workshop on emerging research opportunities in ceramic and glass science was held in September 2016. Reported here are proceedings of the workshop. The report details eight challenges identified through workshop discussions: Ceramic processing: Programmable design and assembly; The defect genome: Understanding, characterizing, and predicting defects across time and length scales; Functionalizing defects for unprecedented properties; Ceramic flatlands: Defining structure-property relations in free-standing, supported, and confined two-dimensional ceramics; Ceramics in the extreme: Discovery and design strategies; Ceramics in the extreme: Behavior of multimaterial systems; Understanding and exploiting glasses and melts under...

  17. The role of ceramic and glass science research in meeting societal challenges: Report from an NSF-sponsored workshop

    Faber, Katherine T.; Asefa, Tewodros; Backhaus-Ricoult, Monika; Brow, Richard; Chan, Julia Y.; Dillon, Shen; Fahrenholtz, William G.; Finnis, Michael W.; Garay, Javier E.; García, R. Edwin; Gogotsi, Yury; Haile, Sossina M.; Halloran, John; Huang, Liping; Jacobsen, Steven D.; Lara-Curzio, Edgar; LeBeau, James; Lee, William E.; Levi, Carlos G.; Levin, Igor; Lewis, Jennifer A.; Lipkin, Don M.; Lu, Kathy; Luo, Jian; Maria, Jon-Paul; Martin, Lane W.; Martin, Steve; Messing, Gary; Navrotsky, Alexandra; Padture, Nitin P.; Randall, Clive; Rohrer, Gregory S.; Rosenflanz, Anatoly; Schaedler, Tobias A.; Schlom, Darrell G.; Sehirlioglu, Alp; Stevenson, Adam J.; Tani, Toshihiko; Tikare, Veena; Trolier-McKinstry, Susan; Wang, Hong; Hu, Juejun; Yildiz, Bilge
    Under the sponsorship of the U.S. National Science Foundation, a workshop on emerging research opportunities in ceramic and glass science was held in September 2016. Reported here are proceedings of the workshop. The report details eight challenges identified through workshop discussions: Ceramic processing: Programmable design and assembly; The defect genome: Understanding, characterizing, and predicting defects across time and length scales; Functionalizing defects for unprecedented properties; Ceramic flatlands: Defining structure-property relations in free-standing, supported, and confined two-dimensional ceramics; Ceramics in the extreme: Discovery and design strategies; Ceramics in the extreme: Behavior of multimaterial systems; Understanding and exploiting glasses and melts under...

  18. Control of hierarchical polymer mechanics with bioinspired metal-coordination dynamics

    Mozhdehi, Davoud; Cheng, Jing; Barrett, Devin G.; Guan, Zhibin; Messersmith, Phillip B.; Grindy, Scott Charles; Learsch, Robert W.; Holten-Andersen, Niels
    In conventional polymer materials, mechanical performance is traditionally engineered via material structure, using motifs such as polymer molecular weight, polymer branching, or block copolymer design. Here, by means of a model system of 4-arm poly(ethylene glycol) hydrogels crosslinked with multiple, kinetically distinct dynamic metal-ligand coordinate complexes, we show that polymer materials with decoupled spatial structure and mechanical performance can be designed. By tuning the relative concentration of two types of metal-ligand crosslinks, we demonstrate control over the material's mechanical hierarchy of energy-dissipating modes under dynamic mechanical loading, and therefore the ability to engineer a priori the viscoelastic properties of these...

  19. Control of hierarchical polymer mechanics with bioinspired metal-coordination dynamics

    Mozhdehi, Davoud; Cheng, Jing; Barrett, Devin G.; Guan, Zhibin; Messersmith, Phillip B.; Grindy, Scott Charles; Learsch, Robert W.; Holten-Andersen, Niels
    In conventional polymer materials, mechanical performance is traditionally engineered via material structure, using motifs such as polymer molecular weight, polymer branching, or block copolymer design. Here, by means of a model system of 4-arm poly(ethylene glycol) hydrogels crosslinked with multiple, kinetically distinct dynamic metal-ligand coordinate complexes, we show that polymer materials with decoupled spatial structure and mechanical performance can be designed. By tuning the relative concentration of two types of metal-ligand crosslinks, we demonstrate control over the material's mechanical hierarchy of energy-dissipating modes under dynamic mechanical loading, and therefore the ability to engineer a priori the viscoelastic properties of these...

  20. The Hierarchical Repeat Sales Model for Granular Commercial Real Estate and Residential Price Indices

    Francke, Marc K; van de Minne, Alexander
    This paper concerns the estimation of granular property price indices in commercial real estate and residential markets. We specify and apply a repeat sales model with multiple stochastic log price trends having a hierarchical additive structure: One common log price trend and cluster specific log price trends in deviation from the common trend. Moreover, we assume that the error terms potentially have a heavy tailed (t) distribution to effectively deal with outliers. We apply the hierarchical repeat sales model on commercial properties in the Philadelphia/Baltimore region and on residential properties in a small part of Amsterdam. The results show that...

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