Planar Chains Research Articles

Spin-polarized transport properties of GdN nanocontacts

Gadolinium nitride (GdN) nanocontacts were recently experimentally shown to be efficient spin filters. Our study is aimed at identifying and analyzing the physical processes responsible for the high spin polarization of the tunneling current in GdN nanostructures. By the example of planar contacts and atomic chains attached to Cu electrodes we assert, using first principle techniques, that a 100% spin-filtering effect can be indeed achieved in GdN nanocontacts. Our analysis shows that the spin filtering is due to the predominant role of nitrogen majority $p$ states in the electron transport, while minority conductance decays exponentially with contact size due to the presence of a minority band gap at the Fermi level. Additionally, GdN zigzag infinite chains are found to be as efficient spin filters as their planar contact counterparts, also exhibiting a 100% spin-filtering effect, which is robust against chain geometry changes.

Thienothiophene-benzotriazole-based semicrystalline linear copolymers for organic field effect transistors

AbstractA series of thienothiophene-benzotriazole-based semicrystalline copolymers, PTTBTz, PTTBTz-F, and PTTBTz-OR, were synthesized by considering chain linearity, planarity and inter-chain packing by virtue of non-covalent attractive interaction. Fluorine and alkoxy substituents were introduced to modulate the intra- and inter-chain coulombic interactions and crystalline ordering. The fluorine and alkoxy-substituted PTTBTz-F and PTTBTz-OR showed pronounced inter-chain packing with edge-on orientation confirmed by UV-vis absorption and X-ray diffraction measurements. The well-resolved diffraction patterns were obtained for PTTBTz-F and PTTBTz-OR, showing (100)∼(500) inter-lamellar scattering peaks (d-spacing, 17∼18 Å) in the out-of-plane direction and a π-π stacking peak (d-spacing, 3.5∼4.1 Å) in the in-plane direction. Organic field effect transistor (OFET) devices were fabricated with a bottom gate and top contact geometry. PTTBTz-F (μh = 4.49 × 10–2 cm2 V–1 s–1, on/off ratio = 1.13 × 107) and PTTBTz-OR (μh = 8.39 × 10–3 cm2 V–1 s–1, on/off ratio = 2.98 × 104) showed nearly 3 and 2 orders of magnitude higher hole mobility upon annealing at 305 and 260 °C, with compared to the unsubstituted PTTBTz.

Metaweaves: sector-way nonreciprocal metasurfaces.

Confluent with the single dimension of time, breach of time-reversal symmetry is usually perceived as a one-dimensional concept. In its ultimate realization-the one-way guiding device-it allows optical propagation in one direction, say +z, and forbids it in the opposite direction -z. Hence, in studies of time-reversal asymmetry the mapping t↦-t is naturally associated with z↦-z. However, strongly nonreciprocal or one-way nanoscale threads can be used to weave metasurfaces thus adding dimensions to this concept. In this new family of surfaces the aforementioned association cannot be made. An example of appropriate threads is the planar one-way particle chains based on the two-type rotation principle. The resulting surfaces-the metaweaves-possess generalized nonreciprocity such as "sector-way" propagation, and offer new possibilities for controlling light in thin surfaces. We study several metaweave designs and their asymmetries in the wave-vector space.

Ln9Al5Sn10: Aluminium Stannides of the Divalent Rare Earth Elements Yb and Eu. Synthesis, Crystal Structure, and Chemical Bonding

AbstractThe isotypic aluminium stannides Ln9Al5Sn10 (Ln = Yb, Eu) are the first ternary compounds in the systems Yb‐Al‐Sn and Eu‐Al‐Sn. They were synthesized in the course of systematic experimental work on the phase stability along the sections LnAl2 – LnSn2 from the elements at maximum temperatures of 1170 K. Their crystal structures were determined using single‐crystal X‐ray diffraction [both monoclinic, space group C2/m, a = 2145.2(5)/2214.99(8), b = 1189.15(14)/1236.67(4), c = 1003.9(2)/1027.57(4) pm, β = 103.22(2)/103.300(3)°, Z = 2, R1 = 0.0492/0.0515 for Ln = Yb/Eu]. The two phases are isotypic to the respective calcium/strontium Al stannides. Their crystal structure can be best described as a complex three‐dimensional network, consisting of three different building units (motifs I, II, and III), which are connected by two‐bonded tin atoms (motif 0). The first motif is a planar zigzag chain of tin like in the CrB‐type structure of e.g. EuSn. Ladders of four‐bonded Al/Sn atoms (motif II) are also present in SrAl2 (KHg2 structure type). The trigonal‐bipyramidal units [Al3Sn2] of motif III, which can alternatively be described as three AlSn4 tetrahedra sharing one common edge, are also known from binary barium aluminides like Ba7Al10. In the Yb compound, this motif III is to a small extent of 17 % statistically substituted by an alternative but related motif IIIB, which consists of only two edge‐sharing AlSn4 tetrahedra. Despite the complex structure and some statistically occupied Al/Sn positions, the chemical bonding in the title compounds can be rationalized using the Zintl concept: Both the interpretation as aluminide/stannides and stannido‐aluminates results in only a minuscule difference between the formal charge of the Al/Sn polyanion and the charge sum of the divalent rare earth cations. FP‐LAPW bandstructure calculations of an ordered subgroup model of the europium compound confirm this interpretation in exhibiting a pronounced minimum of the tDOS slightly below the Fermi level.

Lattice modes in a zigzag crystal of dust particles

A model is presented to explain the normal mode features of dust particles in a planar zigzag crystal chain for the first and second neighbors. The degrees of freedom of particles are the longitudinal and transverse displacements in plane coupled by the first and second neighbor harmonic forces in two dimensions. The constant electric force required for the electrodes to keep the zigzag structure is calculated. The coupling between transverse and longitudinal dust-lattice modes is derived. The latter is considered to be due to the energy of the electrostatic (Yukawa) potential. Moreover, coupled (acoustic and optical) and decoupled (longitudinal and transverse) branches of dust lattice modes for different lattice parameters and structures are studied. Propagation of the longitudinal and acoustic modes is found to be strictly dependent on the value of the distance between the two chains; below that value mode may not propagate Finally it is shown that the frequencies of the acoustic (optical) branches increase (decrease) with increasing distance between the two chains.

Effect of Polymer Chain Folding on the Transition from H- to J-Aggregate Behavior in P3HT Nanofibers

A combination of wavelength-, time-, and polarization-resolved photoluminescence imaging on isolated P3HT nanofibers of varying molecular weight (from 10 to 65 kDa) has revealed a transition in dominant exciton coupling from primarily interchain (H-aggregation) for low molecular weight nanofibers, to predominantly intrachain (J-aggregation) coupling for high molecular weight nanofibers. Based on nanofiber width measurement from TEM imaging, the driving force for this transition appears to be folding of individual polymer chains within the lamellae, resulting in enhanced chain planarity and reduced torsional disorder.

A new family of reconfigurable parallel mechanisms with diamond kinematotropic chain

This paper focuses on a diamond kinematotropic chain which is integrated in the construction of a new family of reconfigurable parallel mechanisms. The branch transition of the planar diamond kinematotropic chain is analyzed and the equivalent kinematic joints corresponding to each motion branch are identified. Kinematic limbs that can provide a constraint force and a constraint couple are enumerated based on screw theory. Sixteen reconfigurable limbs which are capable of decoupling the constraint force and the constraint couple in the reconfigured configurations are constructed by integrating the diamond kinematotropic chain. A family of reconfigurable parallel mechanisms having three identical kinematic limbs is structured by connecting the platform to the base with reconfigurable limbs. The platform of each reconfigurable parallel mechanism has ability to perform variable motion modes such as 3T, 2T1R, 2R1T and 3R. One of the reconfigurable parallel mechanisms is sketched as example and the actuation scheme for the mechanisms in this family is discussed.

The addition of 2,2,2‐trifluoroethanol prevents the aggregation of guanidinium around protein and impairs its denaturation ability: A molecular dynamics simulation study

TFE, 2,2,2-trifluoroethanol, and guanidinium (Gdm(+) ) are two typical osmolytes. A great number of experimental and theoretical studies have shown that TFE and Gdm(+) can accumulate on protein surface and thus exert their effects on protein structure in their respective solutions. Their accumulation manners are, however, different: the hydrophobic property of TFE makes its accumulation more preferential around hydrophobic side chains than other types whereas Gdm(+) prefers to stack strongly against the planar side chains but only weakly binds to the hydrophobic groups. The present molecular dynamics simulation study shows a novel test to investigate the combined effects of TFE and Gdm(+) on protein structure in mixed guanidinium/TFE solution. The results indicate that the accumulation of TFE is more competitive than Gdm(+) in either GdmSCN/TFE or GdmCl/TFE solution. The preceding accumulation of TFE around protein surface limits the approach of Gdm(+) and water to protein. As a result, the hydrogen bonding between Gdm(+) and water to protein is highly forbidden and the secondary structure stability of protein is strongly enhanced. In contrast, without the presence of TFE, the protein structure is largely denatured in similarly concentrated GdmSCN or GdmCl solution.

Density functional theory study of neutral and oxidized thiophene oligomers

The effect of oxidation on the energetics and structure of thiophene (Th) oligomers is studied with density functional theory at the B3PW91∕6-311++G(d,p) level. Neutral n-Th oligomers (2 < n < 13) are gently curved planar chains. Ionization potential and electron affinity results show that n-Th oligomers are easier to be oxidized as their chain length increases. Oxidation states +2, +4, +6, and +8 are energetically stable in 12-Th. Upon oxidation the conjugated backbone of 12-Th switches from extended benzenoid phase to quinoid phase localized on groups of monomers regularly spaced along the chain. Oxidized states +2, +4, +6, and +8 of 12-Th display two +1e localized at the ends of their chains only because of the finite size of the chains. In 12-Th this end-effect extends over the two terminal monomers forming a positive-negative charge duet. This peculiar charge localization makes n-Th oligomers different from other conducting polymers with similar structure, such as polypyrrole. The spectrum of single-electron molecular states of oxidized 12-Th displays two localized single-electron states in the HOMO-LUMO energy gap per +2 oxidation state. Oligothiophene 12-Th doped with F atoms at 1:2 concentration presents a charge transfer of 3.4 e from oligomer to dopants that increases to 4.8 e in the presence of solvent. The charge distribution in these F-doped oligomers is similar to the +4 oxidation state of 12-Th. It is predicted that dopants produce an enhanced charge transfer localized in the proximity of their locations enhancing the formation of bipolarons in the central part of the oligomer chain.

Influence of the bulkiness of the substituent on the aggregation and magnetic properties of poly(3‐alkylthiophene)s

ABSTRACTA series of poly(3‐alkylthiophene)s (P3ATs) (P1–P5) has been synthesized via a Ni(dppp)‐mediated polymerization, varying the bulkiness of the alkyl side chains in order to investigate the influence of the bulkiness of the alkyl substituent on the aggregation and magnetic properties of P3ATs. UV–Vis spectroscopy, performed in solution as well as in film, shows that the stacking of the polymers becomes more complicated as the bulkiness of the side chains increases. Both the π‐interactions and the planarization of the polymer chains are diminished. While aggregation is absent in poor solvent for the polymer with the most bulky side chains, aggregation was present in film, albeit slowed down. This behavior was also confirmed by X‐ray diffraction (XRD) and differential scanning calorimetry (DSC) experiments. Electron spin resonance (ESR) measurements, performed at 300 K on powders, confirmed the trend of decreasing supramolecular order with increasing bulkiness of the side‐chain. Magnetization measurements, performed at 5 and 300 K, are in line with our hypothesis on the influence of π‐interactions and the fraction of planar polymer chains on the coercivity and saturation magnetization, respectively. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 76–86

Molecular structure and electronic properties of a series of oligoalkylthiophenes: A theoretical investigation

Abstract Molecular geometries and electronic properties of 3-alkylthiophenes (ATs) and their oligomers (OATs) are studied by the density functional theory (DFT). Calculations are performed on the oligomers formed by n repeating units, where n ranges from 1 to 6, using the B3LYP/6-31G** level of theory. The results obtained show that the doped oligomers have more satisfactory structural and electronic characteristics for the conducting polymers. The conjugated system in the doped oligomers has more aromaticity, with expanded and planar chains. The calculated energy gap values between the frontal orbitals and also the ionization potential values for the oligomers indicate that with increase in the oligomer chain length, the conductive band gap decreases. Furthermore, our calculations suggest that an electron-donating alkyl substituent at position 3 of the thiophene ring plays an important role in the structural and electronic properties of the polymers.

Quantum Magnons of the Intermediate Phase of Half-Doped Manganite Oxides

At half doping, the ground state of three-dimensional manganite perovskite oxides like R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ca <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , where R is a trivalent ion such as La, Pr, etc., is still unclear. Many experimental findings agree better with the combined magnetic, charge, and orbital order characteristic of the “intermediate phase”, introduced by Efremov in 2004 [Nat. Mater., 3, 853]. This phase consists of spin dimers (thus incorporating aspects of the Zener polaron phase (ZP) proposed in 2002 by Daoud-Aladine [Phys. Rev. Lett., 89, 097205]), though formed by a pair of parallel Mn spins of different magnitude, in principle (thereby allowing for a degree of Mn charge disproportionation: not necessarily as large as that of Mn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -Mn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> in Goodenough's original CE phase [Phys. Rev. 100, 564 (1955)]). In the intermediate phase, consecutive spin dimers localed along the planar zig-zag chains are oriented at a constant relative angle φ between them. Varying Mn-charge disproportionation and φ, the intermediate phase should allow to continuously interpolate between the two limiting cases of the CE phase and the dimer phase denoted as “orthogonal intermediate π/2-phase”. It is not easy to find a microscopic model able to describe the phenomenological intermediate phase adequately for the spin, charge, and orbital degrees of freedom simultaneously. Here, we study the quantum spin excitations of a planar model of interacting localized spins, which we found can stabilize the intermediate phase classically. We compare the quantum magnons of the intermediate phase with those of the CE and orthogonal π/2 phases, in the context of recent experimental results.

Nanoparticle and Process Induced Super Toughened Piezoelectric Hybrid Materials: The Effect of Stretching on Filled System

Process and nanoparticle induced piezoelectric super toughened poly(vinylidene fluoride) (PVDF) nanohybrids have been demonstrated. The nanohybrids have been prepared by incorporating organically modified nanoclay through melt extrusion and solution route. The solution processed nanohybrid exhibit 1100% improvement in toughness as well as adequate stiffness as compared to pure PVDF without any trade-off. The structural and morphological origins of super toughening phenomena have been worked out. The unique crystallization behavior of PVDF on top of the silicate layers (β-phase, planar zigzag chain conformation, and subsequent polar γ-phase and α-phase as layered type) has been revealed to create an island type of structure, which in turn is responsible for greater toughness. The extent of piezoelectric β-phase has been enhanced by controlled stretching of the nanohybrid at moderately high temperature for better disentanglement, and 90% of the piezoelectric phase has been stabilized. The structural change ...

Structure of P3HT in the solid state

ABSTRACTPoly(3‐hexylthiophene) (P3HT) is a polymer widely used in organic photovoltaic devices. Discrepancies in information exist in the literature about its morphological structure in solution and in the solid state. This work is a theoretical study, in which the structure of P3HT in the solid state is deduced from its structure in solution and comparisons with optical absorption data. The results indicate that P3HT is not planar, either in solution or in the solid state. However, the effective conjugation length in the solid state is similar to that of a planar chain. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1350–1354

Identification of complex anions in La1 − x A x MnO3 manganites (A = Ca, Sr) from neutron diffraction data and refinement of their structures on the basis of raman spectroscopy data

The consideration of the Mn(-O…Mn)6 structure unit of the LaMnO3 orthorhombic phase constructed on the basis of neutron diffraction data revealed the presence of atomic groups in the form of (MnO2)− complex anions and separate O2− ions. The Raman spectra have demonstrated that complex anions have a nearly linear O=Mn-O− structure. Comparison of the Raman spectra of the rhombohedral CaMnO3 and BaTiO3 phases and pyramidal molecules of the ZXY2 type has shown that the CaMnO3 phase is composed of pyramidal MnO32− molecules with one Mn=O double bond and two Mn-O− ordinary bonds. The complex anions are linked by O=Mn-O− intermolecular bonds to form planar zigzag Mn=O…Mn chains similar to C=C-C planar chains in some organic compounds exhibiting high electrical conductivity. With decreasing temperature, the Mn…O intermolecular distances decrease, and the Mn=O…Mn chains become even more similar to the C=C-C chains and exhibit high electrical conductivity.

POLYAK TYPE EQUATIONS FOR VIRTUAL ARROW DIAGRAM INVARIANTS IN THE ANNULUS

We describe the space of arrow diagram formulas for virtual knot diagrams in the annulus ℝ × 𝕊1as the kernel of a linear map, inspired from a conjecture due to Polyak. As a main application, we slightly improve Grishanov–Vassiliev's theorem for planar chain invariants.

A molecular design principle of lyotropic liquid-crystalline conjugated polymers with directed alignment capability for plastic electronics

Conjugated polymers with a one-dimensional p-orbital overlap exhibit optoelectronic anisotropy. Their unique anisotropic properties can be fully realized in device applications only when the conjugated chains are aligned. Here, we report a molecular design principle of conjugated polymers to achieve concentration-regulated chain planarization, self-assembly, liquid-crystal-like good mobility and non-interdigitated side chains. As a consequence of these intra- and intermolecular attributes, chain alignment along an applied flow field occurs. This liquid-crystalline conjugated polymer was realized by incorporating intramolecular sulphur-fluorine interactions and bulky side chains linked to a tetrahedral carbon having a large form factor. By optimizing the polymer concentration and the flow field, we could achieve a high dichroic ratio of 16.67 in emission from conducting conjugated polymer films. Two-dimensional grazing-incidence X-ray diffraction was performed to analyse a well-defined conjugated polymer alignment. Thin-film transistors built on highly aligned conjugated polymer films showed more than three orders of magnitude faster carrier mobility along the conjugated polymer alignment direction than the perpendicular direction.

Iodine networks in polyiodides of M(III) urea complexes: Crystal structures of [V(Ur)6][I3]3 and [Dy(Ur)8][I5][I3]2[I2

Unique [V(Ur)6][I3]3 and [Ln(Ur)8][I5][I3]2[I2] (Ln=Dy, La) were prepared by reactions of hexaureavanadium(III) and tetraaquatetraurealanthanide(III) iodides with iodine and the crystal structures of the vanadium and dysprosium compounds are reported. Metal ions are located at the centres of distorted octahedral and square-antiprismatic arrangements, respectively, of oxygen atoms of covalent-coordinated urea. The triiodide anions in the vanadium polyiodide are united in infinite helical chains fitting between the columns of complex cations and binding them together by hydrogen bonding. In the dysprosium polyiodide, the V-shaped I5− ions are united in infinite planar twisting chains. The chains are connected by short contacts through bridging V-shaped I5− ions (combined of I2 molecule and I3− ion) and symmetric I3− ions. Another I3− ion is isolated. The bonded iodine atoms form hexahedral channels, and the columns of the complex cations are localized in these channels and stabilized by hydrogen bonding.

Real-time Estimate of Body Kinematics During a Planar Squat Task Using a Single Inertial Measurement Unit

This study aimed at the real-time estimation of the lower-limb joint and torso kinematics during a squat exercise, performed in the sagittal plane, using a single inertial measurement unit placed on the lower back. The human body was modeled with a 3-DOF planar chain. The planar IMU orientation and vertical displacement were estimated using one angular velocity and two acceleration components and a weighted Fourier linear combiner. The ankle, knee, and hip joint angles were thereafter obtained through a novel inverse kinematic module based on the use of a Jacobian pseudoinverse matrix and null-space decoupling. The aforementioned algorithms were validated on a humanoid robot for which the mechanical model used and the measured joint angles virtually exhibited no inaccuracies. Joint angles were estimated with a maximal error of 1.5°. The performance of the proposed analytical and experimental methodology was also assessed by conducting an experiment on human volunteers and by comparing the relevant results with those obtained through the more conventional photogrammetric approach. The joint angles provided by the two methods displayed differences equal to 3±1°. These results, associated with the real-time capability of the method, open the door to future field applications in both rehabilitation and sport.

Planar Scintigraphic Images Denoising

Scintigraphic images are generally affected by a Poisson type random noise which diminishes qualitatively and quantitatively the images. Restoration techniques aim to “find” an object from one (or several) degraded observation(s). The objective of the restoration is then to produce an image closer to the physical reality. So that the restoration is successful, it is very useful to know the nature of degradation. In this work, we present a planar scintigraphic acquisition chain modeling. This model takes into account the Poisson noise and its stationarity aspect. Then, we present a comparative study of the multi-resolution methods used to reduce the noise in scintigraphic images. Scintigraphy is a tool for exploring functionally several pathologies: the ventricular ejection fraction, the renal clearance and the thyroid activity. Given the fact that scintigraphic images are strongly affected by noise, the objective in this work is to enhance scintigraphic images for a reliable diagnosis and better orientation and understanding of the pathological phenomenon. This paper focuses on two main parts: the first deals with the degradation of model while the second takes into consideration the comparison of the multi-resolution methods for assessing the quality of scintigraphic images to reduce noise using wavelet, contourlet, curvelet, ridgelet and bandelet transformations.