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  • 1
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    American Institute of Physics (AIP)
    Publication Date: 2016-02-25
    Description: We discuss growth and magnetic properties of high-quality two dimensional (2D) Sn 1−x Mn x Se 2 films. Thin films of this 2D ternary alloy with a wide range of Mn concentrations were successfully grown by molecular beam epitaxy. Mn concentrations up to x ≈ 0.60 were achieved without destroying the crystal structure of the parent SnSe 2 2D system. Most important, the specimens show clear weak ferromagnetic behavior above room temperature, which should be of interest for 2D spintronic applications.
    Electronic ISSN: 2166-532X
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  • 2
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    American Institute of Physics (AIP)
    Publication Date: 2016-02-25
    Description: Solution processable semiconductor oxides have opened a new paradigm for the enhancement of the lifetime of thin film solar cells. Their fabrication by low-cost and environmentally friendly solution-processable methods makes them ideal barrier (hole and electron) transport layers. In this work, we fabricate flexible ITO-free organic solar cells (OPV) by printing methods applying an aqueous solution-processed V 2 O 5 as the hole transport layer (HTL) and compared them to devices applying PEDOT:PSS. The transparent conducting electrode was PET/Ag/PEDOT/ZnO, and the OPV configuration was PET/Ag/PEDOT/ZnO/P3HT:PC 60 BM/HTL/Ag. Outdoor stability analyses carried out for more than 900 h revealed higher stability for devices fabricated with the aqueous solution-processed V 2 O 5 .
    Electronic ISSN: 2166-532X
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  • 3
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    American Institute of Physics (AIP)
    Publication Date: 2016-03-02
    Description: We report the experimental observation of longitudinal spin Seebeck effect in a multiferroic helimagnet Ba 0.5 Sr 1.5 Zn 2 Fe 12 O 22 . Temperature gradient applied normal to Ba 0.5 Sr 1.5 Zn 2 Fe 12 O 22 /Pt interface generates inverse spin Hall voltage of spin current origin in Pt, whose magnitude was found to be proportional to bulk magnetization of Ba 0.5 Sr 1.5 Zn 2 Fe 12 O 22 even through the successive magnetic transitions among various helimagnetic and ferrimagnetic phases. This finding demonstrates that the helimagnetic spin wave can be an effective carrier of spin current. By controlling the population ratio of spin-helicity domains characterized by clockwise/counter-clockwise manner of spin rotation with use of poling electric field in the ferroelectric helimagnetic phase, we found that spin-helicity domain distribution does not affect the magnitude of spin current injected into Pt. The results suggest that the spin-wave spin current is rather robust against the spin-helicity domain wall, unlike the case with the conventional ferromagnetic domain wall.
    Electronic ISSN: 2166-532X
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  • 4
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    American Institute of Physics (AIP)
    Publication Date: 2016-03-02
    Description: The magnetoelectric effects are investigated in a cubic compound SrCuTe 2 O 6 , in which uniform Cu 2+ ( S = 1/2) spin chains with considerable spin frustration exhibit a concomitant antiferromagnetic transition and dielectric constant peak at T N ≈ 5.5 K. Pyroelectric J p ( T ) and magnetoelectric current J ME ( H ) measurements in the presence of a bias electric field are used to reveal that SrCuTe 2 O 6 shows clear variations of J p ( T ) across T N at constant magnetic fields. Furthermore, isothermal measurements of J ME ( H ) also develop clear peaks at finite magnetic fields, of which traces are consistent with the spin-flop transitions observed in the magnetization studies. As a result, the anomalies observed in J p ( T ) and J ME ( H ) curves match well with the field-temperature phase diagram constructed from magnetization and dielectric constant measurements, demonstrating that SrCuTe 2 O 6 is a new magnetoelectric compound with S = 1/2 spin chains.
    Electronic ISSN: 2166-532X
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  • 5
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    American Institute of Physics (AIP)
    Publication Date: 2016-03-16
    Description: Polymer nanocomposites are a designer class of materials where nanoscale particles, functional chemistry, and polymer resin combine to provide materials with unprecedented combinations of physical properties. In this paper, we introduce NanoMine, a data-driven web-based platform for analysis and design of polymer nanocomposite systems under the material genome concept. This open data resource strives to curate experimental and computational data on nanocomposite processing, structure, and properties, as well as to provide analysis and modeling tools that leverage curated data for material property prediction and design. With a continuously expanding dataset and toolkit, NanoMine encourages community feedback and input to construct a sustainable infrastructure that benefits nanocomposite material research and development.
    Electronic ISSN: 2166-532X
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  • 6
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    American Institute of Physics (AIP)
    Publication Date: 2016-03-16
    Description: The molecular beam epitaxy (MBE) technique is well known for producing atomically smooth thin films as well as impeccable interfaces in multilayers of many different materials. In particular, molecular beam epitaxy is well suited to the growth of complex oxides, materials that hold promise for many applications. Rapid synthesis and high throughput characterization techniques are needed to tap into that potential most efficiently. We discuss our approach to doing that, leaving behind the traditional one-growth-one-compound scheme and instead implementing combinatorial oxide molecular beam epitaxy in a custom built system.
    Electronic ISSN: 2166-532X
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  • 7
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    American Institute of Physics (AIP)
    Publication Date: 2016-03-16
    Description: Soft matter embodies a wide range of materials, which all share the common characteristics of weak interaction energies determining their supramolecular structure. This complicates structure-property predictions and hampers the direct application of data-driven approaches to their modeling. We present several aspects in which these methods play a role in designing soft-matter materials: drug design as well as information-driven computer simulations, e.g., histogram reweighting. We also discuss recent examples of rational design of soft-matter materials fostered by physical insight and assisted by data-driven approaches. We foresee the combination of data-driven and physical approaches a promising strategy to move the field forward.
    Electronic ISSN: 2166-532X
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  • 8
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    American Institute of Physics (AIP)
    Publication Date: 2016-03-16
    Description: We investigate spin relaxation in graphene by systematically comparing the roles of spin absorption, other contact-induced effects (e.g., fringe fields), and bulk spin relaxation for graphene spin valves with MgO barriers, Al 2 O 3 barriers, and transparent contacts. We obtain effective spin lifetimes by fitting the Hanle spin precession data with two models that include or exclude the effect of spin absorption. Results indicate that additional contact-induced spin relaxation other than spin absorption dominates the contact effect. For tunneling contacts, we find reasonable agreement between the two models with median discrepancy of ∼20% for MgO and ∼10% for Al 2 O 3 .
    Electronic ISSN: 2166-532X
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  • 9
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    American Institute of Physics (AIP)
    Publication Date: 2016-03-16
    Description: Organic-inorganic halide perovskites, especially methylammonium lead halide, have recently led to remarkable advances in photovoltaic devices. However, due to environmental and stability concerns around the use of lead, research into lead-free perovskite structures has been attracting increasing attention. In this study, a layered perovskite-like architecture, (NH 4 ) 3 Bi 2 I 9 , is prepared from solution and the structure solved by single crystal X-ray diffraction. The band gap, which is estimated to be 2.04 eV using UV-visible spectroscopy, is lower than that of CH 3 NH 3 PbBr 3 . The energy-minimized structure obtained from first principles calculations is in excellent agreement with the X-ray results and establishes the locations of the hydrogen atoms. The calculations also point to a significant lone pair effect on the bismuth ion. Single crystal and powder conductivity measurements are performed to examine the potential application of (NH 4 ) 3 Bi 2 I 9 as an alternative to the lead containing perovskites.
    Electronic ISSN: 2166-532X
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  • 10
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    American Institute of Physics (AIP)
    Publication Date: 2016-03-17
    Description: Electrical manipulation of magnetism has been a long sought-after goal to realize energy-efficient spintronics. During the past decade, multiferroic materials combining (anti)ferromagnetic and ferroelectric properties are now drawing much attention and many reports have focused on magnetoelectric coupling effect through strain, charge, or exchange bias. This paper gives an overview of recent progress on electrical manipulation of magnetism through strain-mediated magnetoelectric coupling in multiferroic heterostructures.
    Electronic ISSN: 2166-532X
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  • 11
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    American Institute of Physics (AIP)
    Publication Date: 2016-03-25
    Description: Magnetic interfaces have been identified as promising systems upon which to base next-generation spintronic devices. In these nearly two-dimensional systems, deviations from bulk electronic structure and competition between nearly degenerate magnetic ground states allow the stabilization of widely tunable emergent properties. However, ever smaller length scales pose new challenges which must be overcome in order to understand and control magnetic properties at the atomic level. Using recent examples in oxide heterostructures and topological insulators, we discuss how combining techniques such as neutron scattering, X-ray scattering, X-ray spectroscopy, and transmission electron microscopy enables the probing of magnetism on the Angstrom scale.
    Electronic ISSN: 2166-532X
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  • 12
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    American Institute of Physics (AIP)
    Publication Date: 2016-03-30
    Description: Searchable, interactive, databases of material properties, particularly those relating to functional materials (magnetics, thermoelectrics, photovoltaics, etc.) are curiously missing from discussions of machine-learning and other data-driven methods for advancing new materials discovery. Here we discuss the manual aggregation of experimental data from the published literature for the creation of interactive databases that allow the original experimental data as well additional metadata to be visualized in an interactive manner. The databases described involve materials for thermoelectric energy conversion, and for the electrodes of Li-ion batteries. The data can be subject to machine-learning, accelerating the discovery of new materials.
    Electronic ISSN: 2166-532X
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  • 13
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    American Institute of Physics (AIP)
    Publication Date: 2016-03-19
    Description: Thin films of homogeneous mixture of amorphous silicon and aluminum were produced with magnetron sputtering using 2-phase Al–Si targets. The films exhibited variable compositions, with and without the presence of hydrogen, aSi 1− x Al x and aSi 1− x Al x H y . The structure and optical properties of the films were investigated using transmission electron microscopy, X-ray photoelectron spectroscopy, UV-Vis NIR spectrometry, ellipsometry, and atomistic modeling. We studied the effect of alloying aSi with Al (within the range 0–25 at. %) on the optical band gap, refractive index, transmission, and absorption. Alloying aSi with Al resulted in a non-transparent film with a low band gap ( 1 eV. Variations of the Al and hydrogen content allowed for tuning of the optoelectronic properties. The films are stable up to a temperature of 300 °C. At this temperature, we observed Al induced crystallization of the amorphous silicon and the presence of large Al particles in a crystalline Si matrix.
    Electronic ISSN: 2166-532X
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  • 14
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    American Institute of Physics (AIP)
    Publication Date: 2016-04-01
    Description: The dynamics of a magnetic domain wall (DW) under a transverse magnetic field H y are investigated in two-dimensional (2D) Co/Ni microstrips, where an interfacial Dzyaloshinskii-Moriya interaction (DMI) exists with DMI vector D lying in + y direction. The DW velocity exhibits asymmetric behavior for ± H y ; that is, the DW velocity becomes faster when H y is applied antiparallel to D . The key experimental results are reproduced in a 2D micromagnetic simulation, which reveals that the interfacial DMI suppresses the periodic change of the average DW angle φ even above the Walker breakdown and that H y changes φ , resulting in a velocity asymmetry. This suggests that the 2D DW motion, despite its microscopic complexity, simply depends on the average angle of the DW and thus can be described using a one-dimensional soliton model. These findings provide insight into the magnetic DW dynamics in 2D systems, which are important for emerging spin-orbitronic applications.
    Electronic ISSN: 2166-532X
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  • 15
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    American Institute of Physics (AIP)
    Publication Date: 2016-01-05
    Description: Transport characteristics of TiN/Ta/TaO x /TiN resistive-switching crossbar devices with amorphous TaO x functional layer have been investigated at cryogenic temperatures. Quasi-DC I - V characteristics at 10 K show a negative differential resistance region followed by a rapid transition to the non-volatile formed state. Accounting for Joule heating, the device temperature at the point of switching was estimated at 150 K. Measurements of transient resistance at low stage temperatures revealed an abrupt drop of resistance delayed by a characteristic incubation time after the leading edge of the voltage pulse. The incubation time was a strong function of applied voltage but did not depend on temperature between 10 K and 100 K. This implies a very low activation energy of the threshold switching process at low temperatures. Both of these observations argue against the involvement of oxygen vacancy motion at the onset of the forming process.
    Electronic ISSN: 2166-532X
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  • 16
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    American Institute of Physics (AIP)
    Publication Date: 2016-01-29
    Description: High-mobility perovskite BaSnO 3 films are of significant interest as new wide bandgap semiconductors for power electronics, transparent conductors, and as high mobility channels for epitaxial integration with functional perovskites. Despite promising results for single crystals, high-mobility BaSnO 3 films have been challenging to grow. Here, we demonstrate a modified oxide molecular beam epitaxy (MBE) approach, which supplies pre-oxidized SnO x . This technique addresses issues in the MBE of ternary stannates related to volatile SnO formation and enables growth of epitaxial, stoichiometric BaSnO 3 . We demonstrate room temperature electron mobilities of 150 cm 2 V −1 s −1 in films grown on PrScO 3 . The results open up a wide range of opportunities for future electronic devices.
    Electronic ISSN: 2166-532X
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  • 17
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    American Institute of Physics (AIP)
    Publication Date: 2016-02-02
    Description: The magnetocaloric effect in ferromagnetic single crystal EuTi 0.85 Nb 0.15 O 3 has been investigated using magnetization and heat capacity measurements. EuTi 0.85 Nb 0.15 O 3 undergoes a continuous ferromagnetic phase transition at T C = 9.5 K due to the long range ordering of magnetic moments of Eu 2+ (4 f 7 ). With the application of magnetic field, the spin entropy is strongly suppressed and a giant magnetic entropy change is observed near T C . The values of entropy change Δ S m and adiabatic temperature change Δ T ad are as high as 51.3 J kg −1 K −1 and 22 K, respectively, for a field change of 0–9 T. The corresponding magnetic heating/cooling capacity is 700 J kg −1 . This compound also shows large magnetocaloric effect even at low magnetic fields. In particular, the values of Δ S m reach 14.7 and 23.8 J kg −1 K −1 for field changes of 0–1 T and 0–2 T, respectively. The low-field giant magnetocaloric effect, together with the absence of thermal and field hysteresis makes EuTi 0.85 Nb 0.15 O 3 a very promising candidate for low temperature magnetic refrigeration.
    Electronic ISSN: 2166-532X
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  • 18
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    American Institute of Physics (AIP)
    Publication Date: 2016-02-09
    Description: Structural and transport properties in the normal and superconducting states are investigated in a Ca 0.8 La 0.2 FeAs 2 single crystal with T c = 27 K, belonging to the newly discovered 112 family of iron based superconductors. The transport critical current density J c for both field directions measured in a focused ion beam patterned microbridge reveals a weakly field dependent and low anisotropic behaviour with a low temperature value as high as J c (B = 0) ∼ 10 5 A/cm 2 . This demonstrates not only bulk superconductivity but also the potential of 112 superconductors towards applications. Interestingly, this superconducting compound undergoes a structural transition below 100 K which is evidenced by temperature-dependent X-ray diffraction measurements. Data analysis of Hall resistance and magnetoresistivity indicate that magnetotransport properties are largely dominated by an electron band, with a change of regime observed in correspondence of the onset of a structural transition. In the low temperature regime, the contribution of a hole band to transport is suggested, possibly playing a role in determining the superconducting state.
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  • 19
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    American Institute of Physics (AIP)
    Publication Date: 2016-02-12
    Description: GeTe has been predicted to be the father compound of a new class of multifunctional materials, ferroelectric Rashba semiconductors, displaying a coupling between spin-dependent k-splitting and ferroelectricity. In this paper, we report on epitaxial Fe/GeTe(111) heterostructures grown by molecular beam epitaxy. Spin-pumping experiments have been performed in a radio-frequency cavity by pumping a spin current from the Fe layer into GeTe at the Fe ferromagnetic resonance and detecting the transverse charge current originated in the slab due to spin-to-charge conversion. Preliminary experiments indicate that a clear spin to charge conversion exists, thus unveiling the potential of GeTe for spin-orbitronics.
    Electronic ISSN: 2166-532X
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  • 20
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    American Institute of Physics (AIP)
    Publication Date: 2016-02-24
    Description: We discuss our philosophy for implementation of the Materials Genome Initiative through an integrated materials design strategy, exemplified here in the context of electrocatalytic capture and separation of CO 2 gas. We identify for a group of 1:1 X–N graphene analogue materials that electro-responsive switchable CO 2 binding behavior correlates with a change in the preferred binding site from N to the adjacent X atom as negative charge is introduced into the system. A reconsideration of conductive N-doped graphene yields the discovery that the N-dopant is able to induce electrocatalytic binding of multiple CO 2 molecules at the adjacent carbon sites.
    Electronic ISSN: 2166-532X
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  • 21
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    American Institute of Physics (AIP)
    Publication Date: 2016-03-04
    Description: We observe current induced spin transfer torque resonance in permalloy (Py) grown on monolayer MoS 2 . By passing rf current through the Py/MoS 2 bilayer, field-like and damping-like torques are induced which excite the ferromagnetic resonance of Py. The signals are detected via a homodyne voltage from anisotropic magnetoresistance of Py. In comparison to other bilayer systems with strong spin-orbit torques, the monolayer MoS 2 cannot provide bulk spin Hall effects and thus indicates the purely interfacial nature of the spin transfer torques. Therefore our results indicate the potential of two-dimensional transition-metal dichalcogenide for the use of interfacial spin-orbitronics applications.
    Electronic ISSN: 2166-532X
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  • 22
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    American Institute of Physics (AIP)
    Publication Date: 2016-01-13
    Description: A large remanent polarization close to theoretical value 80 μ C/cm 2 of bulk PbTiO 3 is achieved in epitaxial heterostructures of (120–600)-nm-thick PbTiO 3 films grown by pulsed laser deposition on (001) SrTiO 3 substrate using a 100-nm-thick SrRuO 3 bottom electrode layer. The heterostructures employing a 50-nm-thick electrode exhibit a significantly smaller polarization of ≤60 μ C/cm 2 . A detailed x-ray diffraction analysis of the crystal structure allows for relating this large polarization to electrode-controlled relaxation of epitaxial strain in PbTiO 3 . Based on the observed results, we anticipate that the electrode-promoted strain relaxation can be used to enhance polarization in other epitaxial ferroelectric films.
    Electronic ISSN: 2166-532X
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  • 23
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    American Institute of Physics (AIP)
    Publication Date: 2016-01-21
    Description: We calculate the critical thickness for misfit dislocation (MD) formation in lattice mismatched semipolar and nonpolar III-nitride wurtzite semiconductor layers for the case of MDs originated from prismatic slip (PSMDs). It has been shown that there is a switch of stress relaxation modes from generation of basal slip originated MDs to PSMDs after the angle between c -axis in wurtzite crystal structure and the direction of semipolar growth reaches a particular value, e.g., ∼70° for Al 0.13 Ga 0.87 N/GaN ( h 0 h ̄ 1 ) semipolar heterostructures. This means that for some semipolar growth orientations of III-nitride heterostructures biaxial relaxation of misfit stress can be realized. The results of modeling are compared to experimental data on the onset of plastic relaxation in Al x Ga 1−x N/GaN heterostructures.
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  • 24
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    American Institute of Physics (AIP)
    Publication Date: 2016-02-02
    Description: We report the epitaxial growth and the mechanism of a higher temperature insulator-to-metal-transition (IMT) of vanadium dioxide (VO 2 ) thin films synthesized on aluminum nitride (AlN)/Si (111) substrates by a pulsed-laser-deposition method; the IMT temperature is T IMT ≈ 350 K. X-ray diffractometer and high resolution transmission electron microscope data show that the epitaxial relationship of VO 2 and AlN is VO 2 (010) ‖ AlN (0001) with VO 2 [101] ‖   AlN   [ 2 1 ̄ 1 ̄ 0 ] zone axes, which results in a substrate-induced tensile strain along the in-plane a and c axes of the insulating monoclinic VO 2 . This strain stabilizes the insulating phase of VO 2 and raises T IMT for 10 K higher than T IMT single crystal ≈ 340 K in a bulk VO 2 single crystal. Near T IMT , a resistance change of about four orders is observed in a thick film of ∼130 nm. The VO 2 /AlN/Si heterostructures are promising for the development of integrated IMT-Si technology, including thermal switchers, transistors, and other applications.
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  • 25
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    American Institute of Physics (AIP)
    Publication Date: 2016-02-04
    Electronic ISSN: 2166-532X
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  • 26
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    American Institute of Physics (AIP)
    Publication Date: 2016-02-04
    Description: We report a direct conversion of hexagonal boron nitride (h-BN) into pure cubic boron nitride (c-BN) by nanosecond laser melting at ambient temperatures and atmospheric pressure in air. According to the phase diagram, the transformation from h-BN into c-BN can occur only at high temperatures and pressures, as the hBN-cBN-Liquid triple point is at 3500 K/9.5 GPa. Using nanosecond laser melting, we have created super undercooled state and shifted this triple point to as low as 2800 K and atmospheric pressure. The rapid quenching from super undercooled state leads to formation of super undercooled BN (Q-BN). The c-BN phase is nucleated from Q-BN depending upon the time allowed for nucleation and growth.
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  • 27
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    American Institute of Physics (AIP)
    Publication Date: 2016-02-13
    Description: We discuss and present search strategies for finding new thermoelectric compositions based on first principles electronic structure and transport calculations. We illustrate them by application to a search for potential n -type oxide thermoelectric materials. This includes a screen based on visualization of electronic energy isosurfaces. We report compounds that show potential as thermoelectric materials along with detailed properties, including SrTiO 3 , which is a known thermoelectric, and appropriately doped KNbO 3 and rutile TiO 2 .
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  • 28
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    American Institute of Physics (AIP)
    Publication Date: 2016-02-13
    Description: Through empirical observations, sodium (Na) has been identified as a benign contaminant in some thin-film solar cells. Here, we intentionally contaminate thermally evaporated tin sulfide (SnS) thin-films with sodium and measure the SnS absorber properties and solar cell characteristics. The carrier concentration increases from 2 × 10 16 cm −3 to 4.3 × 10 17 cm −3 in Na-doped SnS thin-films, when using a 13 nm NaCl seed layer, which is detrimental for SnS photovoltaic applications but could make Na-doped SnS an attractive candidate in thermoelectrics. The observed trend in carrier concentration is in good agreement with density functional theory calculations, which predict an acceptor-type Na Sn defect with low formation energy.
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  • 29
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    American Institute of Physics (AIP)
    Publication Date: 2016-02-19
    Description: The past decade has been especially creative for spintronics since the (re)discovery of various two dimensional (2D) materials. Due to the unusual physical characteristics, 2D materials have provided new platforms to probe the spin interaction with other degrees of freedom for electrons, as well as to be used for novel spintronics applications. This review briefly presents the most important recent and ongoing research for spintronics in 2D materials.
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  • 30
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    American Institute of Physics (AIP)
    Publication Date: 2016-01-05
    Description: We report an in situ microbeam grazing incidence X-ray scattering study of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C 8 -BTBT) organic semiconductor thin film deposition by hollow pen writing. Multiple transient phases are observed during the crystallization for substrate temperatures up to ≈93 °C. The layered smectic liquid-crystalline phase of C 8 -BTBT initially forms and preceedes inter-layer ordering, followed by a transient crystalline phase for temperature 〉60 °C, and ultimately the stable phase. Based on these results, we demonstrate a method to produce extremely large grain size and high carrier mobility during high-speed processing. For high writing speed (25 mm/s), mobility up to 3.0 cm 2 /V-s has been observed.
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  • 31
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    American Institute of Physics (AIP)
    Publication Date: 2016-01-05
    Description: For use in high-magnetic-field coil-based applications, the critical current density ( J c ) of REBa 2 Cu 3 O y (REBCO, where RE = rare earth) coated conductors must be isotropically improved, with respect to the direction of the magnetic field; these improvements must be realized at the operating conditions of these applications. In this study, improvement of the J c for various applied directions of magnetic field was achieved by controlling the morphology of the BaHfO 3 (BHO) nano-rods in a SmBCO film. We fabricated the 3.0 vol. % BHO-doped SmBCO film at a low growth temperature of 720 °C, by using a seed layer technique ( T s = 720 °C film). The low-temperature growth resulted in a morphological change in the BHO nano-rods. In fact, a high number density of (3.1 ± 0.1) × 10 3 μ m −2 of small (diameter: 4 ± 1 nm), discontinuous nano-rods that grew in various directions, was obtained. In J c measurements, the J c of the T s = 720 °C film in all directions of the applied magnetic field was higher than that of the non-doped SmBCO film. The J c min (6.4 MA/cm 2 ) of the former was more than 6 times higher than that (1.0 MA/cm 2 ) of the latter at 40 K, under 3 T. The aforementioned results indicated that the discontinuous BHO nano-rods, which occurred with a high number density, exerted a 3D-like flux pinning at the measurement conditions considered. Moreover, at 4.2 K and under 17 T, a flux pinning force density of 1.6 TN/m 3 was realized; this value was comparable to the highest value recorded, to date.
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  • 32
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    American Institute of Physics (AIP)
    Publication Date: 2016-03-23
    Description: The magnetic and transport properties of Fe 3 O 4 films with a series of thicknesses are investigated. For the films with thickness below 15 nm, the saturation magnetization (M s ) increases and the coercivity decreases with the decrease in films’ thickness. The M s of 3 nm Fe 3 O 4 film is dramatically increased to 1017 emu/cm 3 . As for films’ thickness more than 15 nm, M s is tending to be close to the Fe 3 O 4 bulk value. Furthermore, the Verwey transition temperature (T v ) is visible for all the films, but suppressed for 3 nm film. We also find that the ρ of 3 nm film is the highest of all the films. The suppressed T v and high ρ may be related to the islands morphology in 3 nm film. To study the structure, magnetic, and transport properties of the Fe 3 O 4 films, we propose that the giant magnetic moment most likely comes from the spin of Fe ions in the tetrahedron site switching parallel to the Fe ions in the octahedron site at the surface, interface, and grain boundaries. The above results are of great significance and also provide a promising future for either device applications or fundamental research.
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  • 33
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    American Institute of Physics (AIP)
    Publication Date: 2016-03-25
    Description: Materials innovations enable new technological capabilities and drive major societal advancements but have historically required long and costly development cycles. The Materials Genome Initiative (MGI) aims to greatly reduce this time and cost. In this paper, we focus on data reuse in the MGI and, in particular, discuss the impact of three different computational databases based on density functional theory methods to the research community. We also discuss and provide recommendations on technical aspects of data reuse, outline remaining fundamental challenges, and present an outlook on the future of MGI’s vision of data sharing.
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  • 34
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    American Institute of Physics (AIP)
    Publication Date: 2016-03-25
    Description: A Microwave-Induction Heating (MIH) scheme is proposed for the poly(4-vinylphenol) (PVP) gate insulator cross-linking process to replace the traditional oven heating cross-linking process. The cross-linking time is significantly decreased from 1 h to 5 min by heating the metal below the PVP layer using microwave irradiation. The necessary microwave power was substantially reduced to about 50 W by decreasing the chamber pressure. The MIH scheme is a good candidate to replace traditional thermal heating for cross-linking of PVP as the gate insulator for organic thin-film-transistors.
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  • 35
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    American Institute of Physics (AIP)
    Publication Date: 2016-03-29
    Description: Two structural phase transitions are investigated in highly strained BiFeO 3 thin films as a function of film thickness and temperature via synchrotron x-ray diffraction. Both transition temperatures (upon heating: monoclinic M C to monoclinic M A to tetragonal) decrease as the film becomes thinner. A film-substrate interface layer, evidenced by half-order peaks, contributes to this behavior, but at larger thicknesses (above a few nanometers), the temperature dependence results from electrostatic considerations akin to size effects in ferroelectric phase transitions, but observed here for structural phase transitions within the ferroelectric phase. For ultra-thin films, the tetragonal structure is stable to low temperatures.
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  • 36
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    American Institute of Physics (AIP)
    Publication Date: 2016-04-08
    Description: The underlying mechanism behind the blue/red color-switchable luminescence in the C 8 carbon quantum dots (CQDs)/organic hybrid light-emitting devices (LEDs) is investigated. The study shows that the increasing bias alters the energy-level spatial distribution and reduces the carrier potential barrier at the CQDs/organic layer interface, resulting in transition of the carrier transport mechanism from quantum tunneling to direct injection. This causes spatial shift of carrier recombination from the organic layer to the CQDs layer with resultant transition of electroluminescence from blue to red. By contrast, the pure CQDs-based LED exhibits green–red electroluminescence stemming from recombination of injected carriers in the CQDs.
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  • 37
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    American Institute of Physics (AIP)
    Publication Date: 2016-04-08
    Description: Metal organic chemical vapor deposition of GaAs on standard nominal 300 mm Si(001) wafers was studied. Antiphase boundary (APB) free epitaxial GaAs films as thin as 150 nm were obtained. The APB-free films exhibit an improvement of the room temperature photoluminescence signal with an increase of the intensity of almost a factor 2.5. Hall effect measurements show an electron mobility enhancement from 200 to 2000 cm 2 /V s. The GaAs layers directly grown on industrial platform with no APBs are perfect candidates for being integrated as active layers for nanoelectronic as well as optoelectronic devices in a CMOS environment.
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  • 38
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    American Institute of Physics (AIP)
    Publication Date: 2016-04-08
    Description: Mn 0.05 Ge 0.95 quantum dots (QDs) samples were grown by molecular beam epitaxy on Si substrates and 15-nm-thick fully strained Si 0.8 Ge 0.2 virtual substrates, respectively. The QDs samples grown on the Si 0.8 Ge 0.2 virtual substrates show a significant ferromagnetism with a Curie temperature of 227 K, while the QDs samples grown on the Si substrates are non-ferromagnetic. Microstructures of the QDs samples were characterized by high resolution transmission electron microscopy and synchrotron radiation X-ray diffraction. Interdependence between microstructure and ferromagnetism of Mn-doped Ge QDs was investigated. For the QDs sample grown on the strained Si 0.8 Ge 0.2 virtual substrate, although the ferromagnetic phase Mn 5 Ge 3 clusters were found to be formed in small dome-shaped dots, the significant ferromagnetism observed in that sample is attributed to ferromagnetic phase Mn-doped large dome-shaped Ge QDs, rather than to the ferromagnetic phase Mn 5 Ge 3 clusters. The fully strained Si 0.8 Ge 0.2 virtual substrates would result in a residual strain into the QDs and an increase in Ge composition in the QDs. Both consequences favor the formations of ferromagnetic phase Mn-doped Ge QDs from points of view of quantum confinement effect as well as Mn doping at substitutional sites.
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  • 39
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    American Institute of Physics (AIP)
    Publication Date: 2016-04-12
    Description: Single crystals of Mott-Hubbard insulator LaVO 3 exhibit spin and orbital ordering along with a structural change below ≈140 K. The occurrence of orbital ordering in epitaxial LaVO 3 films has, however, been little investigated. By temperature-dependent Raman scattering spectroscopy, we probed and evidenced the transition to orbital ordering in epitaxial LaVO 3 film samples fabricated by pulsed-laser deposition. This opens up the possibility to explore the influence of different epitaxial strain (compressive vs . tensile) and of epitaxy-induced distortions of oxygen octahedra on the orbital ordering, in epitaxial perovskite vanadate films.
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  • 40
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    American Institute of Physics (AIP)
    Publication Date: 2016-04-12
    Description: The process of taking a new material from invention to deployment can take 20 years or more. Since the announcement of the Materials Genome Initiative in 2011, new attention has been paid to accelerating this timeframe to address key challenges in industries from energy, to biomedical materials, to catalysis, to polymers, particularly in the development of new materials discovery techniques. Materials informatics, or algorithmically analyzing materials data at scale to gain novel insight, has been lauded as a path forward in this regard. An equal challenge to discovery, however, is the acceleration from discovery to market. In this paper, we address application of an informatics approach to materials selection, manufacturing, and qualification and identify key opportunities and challenges in each of these areas with a focus on reducing time to market for new advanced materials technologies.
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  • 41
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    American Institute of Physics (AIP)
    Publication Date: 2016-04-14
    Description: In artificial multiferroics hybrids consisting of ferromagnetic La 0.7 Sr 0.3 MnO 3 (LSMO) and ferroelectric BaTiO 3 epitaxial layers, net Ti moments are found from polarized resonant soft x-ray reflectivity and absorption. The Ti dichroic reflectivity follows the Mn signal during the magnetization reversal, indicating exchange coupling between the Ti and Mn ions. However, the Ti dichroic reflectivity shows stronger temperature dependence than the Mn dichroic signal. Besides a reduced ferromagnetic exchange coupling in the interfacial LSMO layer, this may also be attributed to a weak Ti-Mn exchange coupling that is insufficient to overcome the thermal energy at elevated temperatures.
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  • 42
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    American Institute of Physics (AIP)
    Publication Date: 2016-04-21
    Description: In this paper, intrinsic and extrinsic factors dependent switching process in P(VDF-TrFE) thin films is investigated through time domain polarization measurements. The thinning-induced increase of switching time is observed for samples below 80 nm due to the surface oxide layer. For thinner samples the switchable polarization decreases with decreasing temperature since domain pinning prevails. Switching is faster using metal electrode with higher work function, which can be attributed to the lower depolarization field. Furthermore, the switching time increases with increasing the waiting time and increasing the pulse width of the prepolarization pulse caused by imprint effect.
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  • 43
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    American Institute of Physics (AIP)
    Publication Date: 2016-09-20
    Description: We use calorimetry to identify pressure-driven isothermal entropy changes in ceramic samples of the prototypical ferroelectric BaTiO 3 . Near the structural phase transitions at ∼400 K (cubic-tetragonal) and ∼280 K (tetragonal-orthorhombic), the inverse barocaloric response differs in sign and magnitude from the corresponding conventional electrocaloric response. The differences in sign arise due to the decrease in unit-cell volume on heating through the transitions, whereas the differences in magnitude arise due to the large volumetric thermal expansion on either side of the transitions.
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  • 44
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    American Institute of Physics (AIP)
    Publication Date: 2016-09-20
    Description: Nanocrystalline silicon thermoelectrics can be a solution to improve the cost-effectiveness of thermoelectric technology from both material and integration viewpoints. While their figure-of-merit is still developing, recent advances in theoretical/numerical calculations, property measurements, and structural synthesis/fabrication have opened up possibilities to develop the materials based on fundamental physics of phonon transport. Here, this is demonstrated by reviewing a series of works on nanocrystalline silicon materials using calculations of multiscale phonon transport, measurements of interfacial heat conduction, and synthesis from nanoparticles. Integration of these approaches allows us to engineer phonon transport to improve the thermoelectric performance by introducing local silicon-oxide structures.
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  • 45
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    American Institute of Physics (AIP)
    Publication Date: 2016-09-20
    Description: To bring perovskite solar cells to the industrial world, performance must be maintained at the photovoltaic module scale. Here we present large-area manufacturing and processing options applicable to large-area cells and modules. Printing and coating techniques, such as blade coating, slot-die coating, spray coating, screen printing, inkjet printing, and gravure printing (as alternatives to spin coating), as well as vacuum or vapor based deposition and laser patterning techniques are being developed for an effective scale-up of the technology. The latter also enables the manufacture of solar modules on flexible substrates, an option beneficial for many applications and for roll-to-roll production.
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  • 46
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    American Institute of Physics (AIP)
    Publication Date: 2016-09-07
    Description: Due to the high conversion efficiency, organic-inorganic hybrid perovskite (CH 3 NH 3 PbI 3 ) solar cells are investigated for new practical energy resources for our future society. However, the perovskite solar cells have been quite unstable devices. In this manuscript, the history of perovskite solar cells is introduced, and then, the efforts to improve and understand the stability issue of perovskite solar cells are summarized.
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  • 47
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    American Institute of Physics (AIP)
    Publication Date: 2016-09-28
    Description: We take advantage of scanning transmission electron microscopy and electron energy loss spectroscopy to investigate the changes in near-surface electronic structure and quantify the degree of local degradation of Ni-based cathode materials with the layered structure (LiNi 0.8 Mn 0.1 Co 0.1 O 2 and LiNi 0.4 Mn 0.3 Co 0.3 O 2 ) after 20 cycles of delithiation and lithiation. Reduction of transition metals occurs in the near-surface region of cathode materials: Mn is the major element to be reduced in the case of relatively Mn-rich composition, while reduction of Ni ions is dominant in Ni-rich materials. The valences of Ni and Mn ions are complementary, i.e., when one is reduced, the other is oxidized in order to maintain charge neutrality. The depth of degradation zone is found to be much deeper in Ni-rich materials. This comparative analysis provides important insights needed for the devising of new cathode materials with high capacity as well as long lifetime.
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  • 48
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    American Institute of Physics (AIP)
    Publication Date: 2016-10-08
    Description: Metal nanoparticle-semiconductor interfaces are sites of complex light-matter interactions, in particular, the exciton-plasmon coupling which plays a key role in the optical response of such heterostructures. There exists a pathway of photoinduced charge transfer from the semiconductor to the metal, which can be used to controllably vary the driving forces at the interface that leads to tunable optoelectronic properties. In this letter, we report the observation of a dramatic suppression of plasmonic as well as excitonic absorption in a-Ge 24 Se 76 /gold nanoparticle heterostructures by trapped charges. Suppression of the excitonic absorption is strongly correlated with the plasmon wavelength.
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  • 49
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    American Institute of Physics (AIP)
    Publication Date: 2016-10-08
    Description: The elastocaloric effect in a columnar-grained Cu 71.5 Al 17.5 Mn 11 shape memory alloy fabricated by directional solidification was investigated. A large entropy change of 25.0 J/kg K generated by the reversible martensitic transformation was demonstrated. The adiabatic temperature change of 12-13 K was directly measured, covering a wide temperature range of more than 100 K. The low applied stress with a specific elastocaloric ability of 100.8 K/GPa was identified and the potentially attainable operational temperature window as wide as more than 215 K was also discussed. The outstanding elastocaloric refrigeration capability, together with the low applying stress and uniform phase transformation, makes the columnar-grained Cu–Al–Mn shape memory alloy a promising material for solid-state refrigeration.
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  • 50
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    American Institute of Physics (AIP)
    Publication Date: 2016-10-08
    Description: We report the growth of wafer-scale arrays of individually position-controlled and vertically aligned ZnO nanotube arrays on graphene deposited by chemical vapor deposition (CVD-graphene). Introducing two-dimensional layered materials such as graphene as a growth buffer has recently been suggested for growing nanomaterials on traditionally incompatible substrates. However, their growth has been restricted to small areas or had limited controllability. Here, we study the distinct growth behavior of ZnO on CVD-graphene that makes the selective area growth of individual nanostructures on its surface difficult, and propose a set of methods to overcome this. The resulting nanotube arrays, as examined by scanning electron microscopy and transmission electron microscopy, exhibited uniform morphologies and high structural quality over a large area and could be prepared on a broad variety of substrates, including amorphous, metallic, or flexible substrates.
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  • 51
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    American Institute of Physics (AIP)
    Publication Date: 2016-09-21
    Description: With the rapid progress in deposition techniques for hybrid organic-inorganic perovskite (HOIP) thin films, this new class of photovoltaic (PV) technology has achieved material quality and power conversion efficiency comparable to those established technologies. Among the various techniques for HOIP thin films preparation, vapor based deposition technique is considered as a promising alternative process to substitute solution spin-coating method for large-area or scale-up preparation. This technique provides some unique benefits for high-quality perovskite crystallization, which are discussed in this research update.
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  • 52
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    American Institute of Physics (AIP)
    Publication Date: 2016-09-21
    Description: We report the significant increase in the electrical conductivity, by five orders of magnitude, of Re-doped β -MoO 3 epitaxial films grown using reactive DC magnetron sputtering. Re atoms were successfully incorporated into the films by using Mo-Re alloy targets, although the film compositions deviated significantly from those of the targets. Pristine β -MoO 3 exhibited a conductivity below 10 −7 S/cm, whereas β -Mo 0.982 Re 0.018 O 3 exhibited a conductivity of 1.2 × 10 −2 S/cm and a high optical transmittance of 67% (average) in the visible region. Furthermore, transparent conducting properties were reproduced in a polycrystalline film grown on a glass substrate, indicating the high potential of these films for use as transparent conductors.
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  • 53
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    American Institute of Physics (AIP)
    Publication Date: 2016-10-04
    Description: First order magnetocaloric materials reach high entropy changes but at the same time exhibit hysteresis losses which depend on the sample’s microstructure. We use non-destructive 3D X-ray microtomography to understand the role of surface morphology for the magnetovolume transition of LaFe 11.8 Si 1.2 . The technique provides unique information on the spatial distribution of the volume change at the transition and its relationship with the surface morphology. Complementary Hall probe imaging confirms that on a morphologically complex surface minimization of strain energy dominates. Our findings sketch the way for a tailored surface morphology with low hysteresis without changing the underlying phase transition.
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  • 54
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    American Institute of Physics (AIP)
    Publication Date: 2016-10-04
    Description: The power conversion efficiency of lead halide perovskite solar cells recently surpassed 22.1%. In this study, we suggest the perovskite absorber growth mechanism of the two-step process could be explained by an Ostwald ripening growth model for planar-structure perovskite solar cells. We attempt to find out the source of two main problems such as unreacted PbI 2 and non-uniformed morphology by the proposed ripening growth mechanism and experimental results. This growth mechanism opens the way toward understanding a key aspect of the photovoltaic operation of high-efficiency, two-step perovskite solar cells.
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  • 55
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    American Institute of Physics (AIP)
    Publication Date: 2016-10-05
    Description: The conventional mechanoluminescence (ML) mechanism of phosphors such as SrAl 2 O 4 :Eu and ZnS:Mn is known to utilize carrier trapping at shallow traps followed by stress (or strain)-induced detrapping, which leads to activator recombination in association with local piezoelectric fields. However, such a conventional ML mechanism was found to be invalid for the ZnS:Cu-embedded polydimethylsiloxane (PDMS) composite, due to the absence of luminescence with a rigid matrix and a negligibly small value of the piezoelectric coefficient (d 33 ) of the composite. An alternative mechanism, namely, the triboelectricity-induced luminescence has been proposed for the mechanically driven luminescence of a ZnS:Cu-PDMS composite.
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  • 56
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    American Institute of Physics (AIP)
    Publication Date: 2016-10-11
    Description: Ex situ analyses on topological insulator films require protection against surface contamination during air exposure. This work reports on a technique that combines deposition of protective capping just after epitaxial growth and its mechanical removal inside ultra-high vacuum systems. This method was applied to Bi 2 Te 3 films with thickness varying from 8 to 170 nm. Contrarily to other methods, this technique does not require any sputtering or thermal annealing setups installed inside the analyzing system and preserves both film thickness and surface characteristics. These results suggest that the technique presented here can be expanded to other topological insulator materials.
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  • 57
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    American Institute of Physics (AIP)
    Publication Date: 2016-10-11
    Description: We used high-resolution Kelvin probe force microscopy (KPFM) to investigate the immobilization of a prostate specific antigen (PSA) antibody by measuring the surface potential (SP) on a MoS 2 surface over an extensive concentration range (1 pg/ml–100 μ g/ml). After PSA antibody immobilization, we demonstrated that the SP on the MoS 2 surface characterized by KPFM strongly correlated to the electrical signal of a MoS 2 bioFET. This demonstration can not only be used to optimize the immobilization conditions for captured molecules, but can also be applied as a diagnostic tool to complement the electrical detection of a MoS 2 FET biosensor.
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  • 58
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    American Institute of Physics (AIP)
    Publication Date: 2016-10-18
    Description: Direct conversion between thermal and electrical energy can be achieved by thermoelectric materials, which provide a viable route for power generation and solid state refrigeration. Here, we use a combination of energetic, electronic, and vibrational first-principles based results to predict the figure of merit performance in hole doped single crystals of SnS and (Pb,Sn)S. We find high ZT values for both materials, specifically for (Pb,Sn)S along the b -axis. Both SnS and (Pb,Sn)S have excellent power factors when doped, due to a combination of increased electrical conductivity (due to doping) and a significantly enhanced Seebeck coefficient obtained by a doping-induced multiband effect. Anharmonic phonon calculations combined with a Debye-Calloway model show that the lattice thermal conductivity of both compounds is low, due to intrinsic anharmonicity, and is lowered further by the random, solid solution nature of the cation sublattice of (Pb,Sn)S. (Pb,Sn)S exhibits a high ZT plateau ranging from 1.3 at 300 K to 1.9 at 800 K. The overall ZT of the hole doped (Pb,Sn)S crystals is predicted to outperform most of the current state-of-the-art thermoelectric sulfide materials.
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  • 59
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    American Institute of Physics (AIP)
    Publication Date: 2016-11-18
    Description: We use micro-Raman spectroscopy to study strain in free-standing graphene monolayers anchored to SiN holes of non-circular geometry. We show that a uniform differential pressure load yields measurable deviations from hydrostatic strain, conventionally observed in radially symmetric microbubbles. A pressure load of 1 bar yields a top hydrostatic strain of ≈ 0.7% and a G ± splitting of 10 cm −1 in graphene clamped to elliptical boundaries with axes 40 and 20 μ m, in good agreement with the calculated anisotropy Δ ε ≈ 0.6% and consistently with recent reports on Grüneisen parameters. The implementation of arbitrary strain configurations by designing suitable boundary clamping conditions is discussed.
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  • 60
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    American Institute of Physics (AIP)
    Publication Date: 2016-11-22
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  • 61
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    American Institute of Physics (AIP)
    Publication Date: 2016-11-29
    Description: We report the fabrication of a set of new rare-earth-free magnetic compounds, which form the Fe 3 Co 3 Ti 2 -type hexagonal structure with P -6 m 2 symmetry. Neutron powder diffraction shows a significant Fe/Co anti-site mixing in the Fe 3 Co 3 Ti 2 structure, which has a strong effect on the magnetocrystalline anisotropy as revealed by first-principle calculations. Increasing substitution of Fe atoms for Co in the Fe 3 Co 3 Ti 2 lattice leads to the formation of Fe 4 Co 2 Ti 2 , Fe 5 CoTi, and Fe 6 Ti 2 with significantly improved permanent-magnet properties. A high magnetic anisotropy (13.0 Mergs/cm 3 ) and saturation magnetic polarization (11.4 kG) are achieved at 10 K by altering the atomic arrangements and decreasing Fe/Co occupancy disorder.
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  • 62
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    American Institute of Physics (AIP)
    Publication Date: 2016-12-01
    Description: Carrier multiplication using singlet exciton fission (SF) to generate a pair of spin-triplet excitons from a single optical excitation has been highlighted as a promising approach to boost the photocurrent in photovoltaics (PVs) thereby allowing PV operation beyond the Shockley-Queisser limit. The applicability of many efficient fission materials, however, is limited due to their poor solubility. For instance, while acene-based organics such as pentacene (Pc) show high SF yields (up to200%), the plain acene backbone renders the organic molecule insoluble in common organic solvents. Previous approaches adding solubilizing side groups such as bis(tri- iso -propylsilylethynyl) to the Pc core resulted in low vertical carrier mobilities due to reduction of the transfer integrals via steric hindrance, which prevented high efficiencies in PVs. Here we show how to achieve good solubility while retaining the advantages of molecular Pc by using a soluble precursor route. The precursor fully converts into molecular Pc through thermal removal of the solubilizing side groups upon annealing above 150 °C in the solid state. The annealed precursor shows small differences in the crystallinity compared to evaporated thin films of Pc, indicating that the Pc adopts the bulk rather than surface polytype. Furthermore, we identify identical SF properties such as sub-100 fs fission time and equally long triplet lifetimes in both samples.
    Electronic ISSN: 2166-532X
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  • 63
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    American Institute of Physics (AIP)
    Publication Date: 2016-12-08
    Description: We record the two-dimensional laser-induced fluorescence (LIF) on multiple plasma constituents in a YBiO 3 plasma. This allows us to directly link the influence of oxygen present in the background gas during pulsed laser deposition to the oxidation of plasma species as well as the formation of epitaxial YBiO 3 films. With spatiotemporal LIF mapping of the plasma species (Y, YO, Bi, and BiO) in different background gas compositions, we find that little direct chemical interaction takes place between the plasma plume constituents and the background gas. However, a strong influence of the background gas composition can be seen on the YBO film growth, as well as a strong correlation between the oxygen fraction in the background gas and the amount of YO in the plasma plume. We assign this correlation to a direct interaction between the background gas and the target in between ablation pulses. In an O 2 background, an oxygen-rich surface layer forms in between ablation pulses, which provides additional oxygen for the plasma plume during target ablation. This differs from our previous observations in STO and LAO plasmas, where species oxidation primarily takes place during propagation of the plasma plume towards the substrate.
    Electronic ISSN: 2166-532X
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  • 64
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    American Institute of Physics (AIP)
    Publication Date: 2016-10-05
    Description: All-oxide photovoltaics could open rapidly scalable manufacturing routes, if only oxide materials with suitable electronic and optical properties were developed. SnO has exceptional doping and transport properties among oxides, but suffers from a strongly indirect band gap. Here, we address this shortcoming by band-structure engineering through isovalent but heterostructural alloying with divalent cations (Mg, Ca, Sr, and Zn). Using first-principles calculations, we show that suitable band gaps and optical properties close to that of direct semiconductors are achievable, while the comparatively small effective masses are preserved in the alloys. Initial thin film synthesis and characterization support the feasibility of the approach.
    Electronic ISSN: 2166-532X
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  • 65
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    American Institute of Physics (AIP)
    Publication Date: 2016-10-19
    Description: Double perovskite Bi 2 FeMnO 6 is a potential candidate for the single-phase multiferroic system. In this work, we study the magnetic, electronic, and optical properties in BFMO by performing the density functional theory calculations and experimental measurements of magnetic moment. We also demonstrate the strain dependence of magnetization. More importantly, our calculations of electronic and optical properties reveal that the onsite local correlation on Mn and Fe sites is critical to the gap opening in BFMO, which is a prerequisite condition for the ferroelectric ordering. Finally, we calculate the x-ray magnetic circular dichroism spectra of Fe and Mn ions (L 2 and L 3 edges) in BFMO.
    Electronic ISSN: 2166-532X
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  • 66
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    American Institute of Physics (AIP)
    Publication Date: 2016-10-28
    Electronic ISSN: 2166-532X
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  • 67
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    American Institute of Physics (AIP)
    Publication Date: 2016-11-02
    Description: CdTe defect chemistry is adjusted by annealing samples with excess Cd or Te vapor with and without extrinsic dopants. We observe that Group I (Cu and Na) elements can increase hole density above 10 16 cm −3 , but compromise lifetime and stability. By post-deposition incorporation of a Group V dopant (P) in a Cd-rich ambient, lifetimes of 30 ns with 10 16 cm −3 hole density are achieved in single-crystal and polycrystalline CdTe without CdCl 2 or Cu. Furthermore, phosphorus doping appears to be thermally stable. This combination of long lifetime, high carrier concentration, and improved stability can help overcome historic barriers for CdTe solar cell development.
    Electronic ISSN: 2166-532X
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  • 68
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    American Institute of Physics (AIP)
    Publication Date: 2016-11-02
    Description: We report the first example of room-temperature rubber-like deformation in thin-film metallic glasses (TFMGs), 260-nm-thick Zr 60 Cu 24 Al 11 Ni 5 layers, under ultra-high shear strain. The TFMGs were deposited, with no external heating, on Zr-based bulk metallic glass (BMG) and Si(001) substrates by rf magnetron sputtering in a 3 mTorr Ar plasma. Cross-sectional transmission electron microscopy (XTEM) analyses and nanoindentation results reveal that the TFMGs undergo an incredibly large shear strain, estimated to be ∼4000%, during fatigue tests, and thickness reductions of up to 61.5%, with no shear-banding or cracking, during extreme nanoindentation experiments extending through the film and into the substrate. TFMG/BMG samples also exhibit film/substrate diffusion bonding during deformation as shown by high-resolution XTEM.
    Electronic ISSN: 2166-532X
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  • 69
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    American Institute of Physics (AIP)
    Publication Date: 2016-11-08
    Description: In this work, combining experimental results and first principles calculations, we show that interstitial nitrogen not only serves for inducing tetragonality in α ′-Fe 8 N x but is also essential for achieving a high degree of perpendicular magneto-crystalline anisotropy, K . Our results demonstrate that the orbital magnetic moments of the iron atoms above and below N in the direction of magnetization are much more susceptible to the applied magnetic field than their in-plane counterparts, leading to a giant value of K as compared to a hypothetical distorted material without N.
    Electronic ISSN: 2166-532X
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  • 70
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    American Institute of Physics (AIP)
    Publication Date: 2016-11-09
    Description: Time domain electric pulse measurements were conducted on a capacitor consisting of a Pt film as the top electrode, atomic-layer-deposited 6.5-nm-thick amorphous Al 2 O 3 as the dielectric layer, and two-dimensional electron gas (2DEG) at the interface between Al 2 O 3 and SrTiO 3 as the bottom electrode. The sample showed highly useful current-voltage characteristics as the selector in cross-bar array resistance switching random access memory. The long-term (order of second) variation in the leakage current when the Pt electrode was positively biased was attributed to the field-induced migration of oxygen vacancies between the interior of the Al 2 O 3 and the 2DEG region. Relaxation of the vacancy concentration occurred even at room temperature.
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  • 71
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    American Institute of Physics (AIP)
    Publication Date: 2016-11-15
    Description: We investigate the electromechanical interactions in individual polyvinylidene fluoride-trifluoroethylene nanowires in response to localized electrical poling via a conducting atomic force microscope tip. Spatially resolved measurements of piezoelectric coefficients and elastic moduli before and after poling reveal a striking dependence on the polarity of the poling field, notably absent in thin films of the same composition. These observations are attributed to the unclamped nature of the nanowires and the inherent asymmetry in their chemical and electrical interactions with the tip and underlying substrate. Our findings provide insights into the mechanism of poling/switching in polymer nanowires critical to ferroelectric device performance.
    Electronic ISSN: 2166-532X
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  • 72
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    American Institute of Physics (AIP)
    Publication Date: 2016-11-22
    Description: We report a method in making transmission electron microscopy sample for both CVD-grown and exfoliated 2D materials without etching process, thus gentle to those 2D materials that are sensitive to water and reactive etchants. Large-scale WS 2 monolayer grown on glass, NbS 2 atomic layers grown on exfoliated h-BN flakes, and water-sensitive exfoliated TiS 2 flakes are given as representative examples. We show that the as-transferred samples not only retain excellent structural integrity down to atomic scale but also have little oxidations, presumably due to the minimum contact with water/etchants. This method paves the way for atomic scale structural and chemical investigations in sensitive 2D materials.
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  • 73
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    American Institute of Physics (AIP)
    Publication Date: 2016-11-01
    Description: The temperature dependence of the thermal conductivity of 27 different single crystal oxides is reported from ≈20 K to 350 K. These crystals have been selected among the most common substrates for growing epitaxial thin-film oxides, spanning over a range of lattice parameters from ≈3.7 Å to ≈12.5 Å. Different contributions to the phonon relaxation time are discussed on the basis of the Debye model. This work provides a database for the selection of appropriate substrates for thin-film growth according to their desired thermal properties, for applications in which heat management is important.
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  • 74
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    American Institute of Physics (AIP)
    Publication Date: 2016-11-05
    Description: Using atomistic simulations, several semi-coherent cube-on-cube bimetal interfaces are comparatively investigated to unravel the combined effect of the character of misfit dislocations, the stacking fault energy difference between bimetal pairs, and their lattice mismatch on the dissociation of interfacial misfit dislocations. Different dissociation paths and features under loadings provide several unique deformation mechanisms that are critical for understanding interface strengthening. In particular, applied strains can cause either the formation of global interface coherency by the migration of misfit dislocations from an interface to an adjoining crystal interior or to an alternate packing of stacking faults connected by stair-rod dislocations.
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  • 75
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    American Institute of Physics (AIP)
    Publication Date: 2016-11-09
    Description: We present a first evaluation of the potential for spin crossover (SCO) compounds to be considered as a new class of giant mechanocaloric effect materials. From literature data on the variation of the spin crossover temperature with pressure, we estimate the maximum available adiabatic temperature change for several compounds and the relatively low pressures that may be required to observe these effects.
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  • 76
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    American Institute of Physics (AIP)
    Publication Date: 2016-11-11
    Description: We study the effect of self-assembled monolayer (SAM) treatment of the SiO 2 dielectric on the electrical characteristics of PbS transistors. Using SAMs, we observe threshold voltage shifts in the electron transport, allowing us to tune the electrical properties of the devices depending on the SAM molecule used. Moreover, the use of a specific SAM improves the charge carrier mobility in the devices by a factor of three, which is attributed to the reduced interface traps due to passivated silanol on the SiO 2 surface. These reduced traps confirm that the voltage shifts are not caused by the trap states induced by the SAMs.
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  • 77
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    American Institute of Physics (AIP)
    Publication Date: 2016-11-29
    Description: We devised a single-step mechanochemical synthesis/densification procedure for Cu 2 X (X = S, Se) thermoelectric materials via applying a pressure of 3 GPa to a stoichiometric admixture of elemental Cu and X for 3 min at room temperature. The obtained bulk materials were single-phase, nearly stoichiometric structures with a relative packing density of 97% or higher. The structures contained high concentration of atomic scale defects and pores of 20-200 nm diameter. The above attributes gave rise to a high thermoelectric performance: at 873 K, the ZT value of Cu 2 S reached 1.07, about 2.1 times the value typical of samples grown from the melt. The ZT value of Cu 2 Se samples reached in excess of 1.2, close to the state-of-the-art value.
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  • 78
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    American Institute of Physics (AIP)
    Publication Date: 2016-12-07
    Description: The structure and luminescence mechanisms of the CuInS 2 quantum dots (QDs) after epitaxial growth of ZnS shell are in debate. The light absorption/emission spectroscopy reveals that after ZnS shell growth the cation diffusion at the CuInS 2 /ZnS interface results in formation of the alloyed Cu x Zn 1− x InS 2 /ZnS:Cu QDs. These core/shell QDs exhibit dual-color photoluminescence with abnormal blue shift with decreasing excitation photon energy. The results show that the green and orange emissions originate separately from defects in the core and the shell. The absorption tail of the ZnS QDs turns from Urbach to Halperin-Lax type after Cu doping.
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  • 79
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    American Institute of Physics (AIP)
    Publication Date: 2016-08-05
    Description: The electronic structure of Heusler alloys having mixed magnetic phases, comprising of vicinal anti-ferromagnetic and ferromagnetic orders, is of great significance. We present the results of an electronic structure study on Ni x Cu 1− x MnSb Heusler alloys, using Mn-2p core-level photoemission spectroscopy. Room temperature data in the paramagnetic phase reveal a non-monotonic variation of both electron correlation strength and conduction-band hybridization such that the former enhances while the latter weakens for compositions showing a mixed phase relative to compositions at the phase boundaries to the ordered phases. The results suggest a possible electronic driving force for settling mixed-magnetic phases.
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  • 80
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    American Institute of Physics (AIP)
    Publication Date: 2016-08-11
    Description: We present a detailed study of compressively strained Pb x Sr 1− x TiO 3 thin films grown by off-axis radio frequency magnetron sputtering on (001)-oriented Nb-doped SrTiO 3 substrates. Film tetragonality and the ferroelectric critical temperatures are measured for samples of different composition and thickness and compared with a phenomenological Landau-Devonshire model. 180 ∘ ferroelectric domains are observed using both X-ray diffraction and piezoresponse force microscopy and domain sizes obtained by the two techniques are compared and discussed.
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  • 81
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    American Institute of Physics (AIP)
    Publication Date: 2016-08-20
    Description: Lead halide perovskite solar cells have shown a tremendous rise in power conversion efficiency with reported record efficiencies of over 20% making this material very promising as a low cost alternative to conventional inorganic solar cells. However, due to a differently severe “hysteretic” behaviour during current density-voltage measurements, which strongly depends on scan rate, device and measurement history, preparation method, device architecture, etc., commonly used solar cell measurements do not give reliable or even reproducible results. For the aspect of commercialization and the possibility to compare results of different devices among different laboratories, it is necessary to establish a measurement protocol which gives reproducible results. Therefore, we compare device characteristics derived from standard current density-voltage measurements with stabilized values obtained from an adaptive tracking of the maximum power point and the open circuit voltage as well as characteristics extracted from time resolved current density-voltage measurements. Our results provide insight into the challenges of a correct determination of device performance and propose a measurement protocol for a reliable characterisation which is easy to implement and has been tested on varying perovskite solar cells fabricated in different laboratories.
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  • 82
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    American Institute of Physics (AIP)
    Publication Date: 2016-08-20
    Description: We report on synthesis and characterization of a new magnetic nanolaminate (V,Mn) 3 GaC 2 , which is the first magnetic MAX phase of a 312 stoichiometry. Atomically resolved energy dispersive X-ray mapping of epitaxial thin films reveals a tendency of alternate chemical ordering between V and Mn, with atomic layers composed of primarily one element only. Magnetometry measurements reveal a ferromagnetic response between 50 K and 300 K, with indication of a magnetic ordering temperature well above room temperature.
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  • 83
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    American Institute of Physics (AIP)
    Publication Date: 2016-08-23
    Description: We have developed a method to detect the presence of small amounts of chemical substances in water, using a Al 2 O 3 nanoparticle thin film covered with phosphonic acid (HDF-PA) self-assembled monolayer. The HDF-PA self-assembled Al 2 O 3 nanoparticle thin film acts as a liquid-vapour separation filter, allowing the passage of chemical vapour while blocking liquids. Prevention of the liquid from contacting the SnO 2 nanowire and source-drain electrodes is required in order to avoid abnormal operation. Using this characteristic, the concentration of chemical substances in water could be evaluated by measuring the current changes in the SnO 2 nanowire transistor covered with the HDF-PA self-assembled Al 2 O 3 nanoparticle thin film.
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  • 84
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    American Institute of Physics (AIP)
    Publication Date: 2016-08-23
    Description: Pb 0.9 La 0.1 (Zr 0.52 Ti 0.48 )O 3 (PLZT) relaxor-ferroelectric thin films were grown on SrRuO 3 /SrTiO 3 /Si substrates by pulsed laser deposition. A large recoverable storage density ( U reco ) of 13.7 J/cm 3 together with a high energy efficiency ( η ) of 88.2% under an applied electric field of 1000 kV/cm and at 1 kHz frequency was obtained in 300-nm-thick epitaxial PLZT thin films. These high values are due to the slim and asymmetric hysteresis loop when compared to the values in the reference undoped epitaxial lead zirconate titanate Pb(Zr 0.52 Ti 0.48 )O 3 ferroelectric thin films ( U reco = 9.2 J/cm 3 and η = 56.4%) which have a high remanent polarization and a small shift in the hysteresis loop, under the same electric field.
    Electronic ISSN: 2166-532X
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