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Influence of the Supramolecular Arrangement in the Electrical Conductivity of Poly(thiophene) Thin Films
摘要： Thin ?lms of regioregular polythiophene derivatives have had their optical, structural and morphological properties characterized, but there is still a lack of comparative studies to determine the effect from deposition techniques, especially on the electrical properties. In this study, we produced Langmuir-Schaefer and spin-coated ?lms of regioregular alkyl-substituted polythiophene derivatives (P3AT) to investigate how distinct supramolecular arrangements can affect their properties. The Langmuir-Schaefer ?lms deposited on indium-tin oxide substrates were observed to grow linearly with the number of layers, according to UV-visible absorption spectroscopy. Atomic force microscopy and Brewster angle microscopy were carried out for morphological characterization. From electrical transport measurements, the DC electrical conductivity of Langmuir-Schaefer ?lms of P3AT was higher than the corresponding spin-coated ?lms, which can be related to the dissimilar roughness and molecular-level organization provided by the Langmuir-Schaefer technique.
关键词： Electrical Conductivity,Langmuir-Schaefer,Polythiophene
更新于2025-09-04 15:30:14
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The effects of curvature on the thermal conduction of bent silicon nanowire
摘要： Curvature induced by mechanical deformation in nanostructures has been found to significantly affect their stability and reliability during applications. In this work, we investigated the effects of curvature induced by mechanical bending on the thermal properties of silicon nanowire (SiNW) by using molecular dynamics simulations. By examining the relationship between the curved geometry and local temperature/heat flux distribution, we found that there is no temperature gradient/heat flux along the radial direction of the bent SiNW, and the local heat current density along the circumferential direction varies with the radius of curvature. Interestingly, a ～10% reduction in the thermal conductivity is found in the bent SiNW due to the depression of long-wavelength phonons caused by its inhomogeneous deformation. The present work demonstrates that the curvature induced by mechanical bending can be used to modulate the thermal conductivity of SiNWs.
关键词： thermal conductivity,curvature,silicon nanowire,thermal conduction,molecular dynamics simulations
更新于2025-09-04 15:30:14
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Effect of Annealing Temperature on Morphology and Electrical Property of Hydrothermally-Grown ZnO Nanorods/ <i>p</i> -Si Heterojunction Diodes
摘要： In this study, ZnO nanorods (NRs) were synthesized using the hydrothermal method, and the effects of annealing temperature (150 °C–600 °C) on morphology, crystallinity, defects states of the NRs, and electrical property of the n-type ZnO NRs/p-type Si heterojunction diodes were investigated. No appreciable changes in the morphology and crystal structure of the ZnO NRs were observed with increasing annealing temperature up to 450 °C. As the temperature increased to 600 °C, the average length and diameter of the NRs decreased due to the partial melting and sintering in the NRs. From the X-ray photoelectron spectroscopy (XPS) results, the concentration of internal oxygen vacancies decreased with increasing annealing temperature to 450 °C due to thermal diffusion of oxygen vacancies to the surface. The electrical conductivity of the NRs increased to 450 °C, which was attributed to the increased crystallinity and low defects concentration (oxygen vacancy) in the NRs. Conversely, the electrical conductivity degraded at 600 °C due to the decreased effective contact area.
关键词： Annealing,Hydrothermal Process,pn Heterojunction,Electrical Conductivity,ZnO
更新于2025-09-04 15:30:14
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Designing Conjugated Polymers for Molecular Doping: The Roles of Crystallinity, Swelling, and Conductivity in Sequentially-Doped Selenophene-Based Copolymers
摘要： Although chemical doping is widely used to tune the optical and electrical properties of semiconducting polymers, it is not clear how the degree of doping and the electrical properties of the doped materials vary with the bandgap, valence band level, and crystallinity of the polymer. We address this question utilizing a series of statistical copolymers of poly(3-hexylthiophene) (P3HT) and poly(3-heptylselenophene) (P37S) with controlled gradients in bandgap, valence band position and variable crystallinity. We dope the copolymers in our series with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) using solution sequential processing (SqP). We then examine the structures of the films using grazing incidence wide-angle x-ray scattering (GIWAXS), differential scanning calorimetry (DSC) and ellipsometric porosimetry, and the electrical properties of the films via the AC Hall effect. We find that the ability of a particular copolymer to be doped is largely determined by the offset of the polymer’s valence band energy level relative to the LUMO of F4TCNQ. The ability of the carriers created by doping to be highly mobile and thus contribute to the electrical conductivity, however, is controlled by how well the polymer can incorporate the dopant into its crystalline structure, which is in turn influenced by how well it can be swelled by the solvent used for dopant incorporation. The interplay of these effects varies in a non-monotonic way across our thiophene:selenophene copolymer series. The position and shape of the polaron absorption spectrum correlate well with the polymer crystallinity and carrier mobility, but the polaron absorption amplitude does not reflect the number of mobile carriers, precluding the use of optical spectroscopy to accurately estimate the mobile carrier concentration. Overall, we find that the degree of crystallinity of the doped films is what best correlates with conductivity, suggesting that only carriers in crystalline regions of the film, where the dopant counterions and polarons are forced apart by molecular packing constraints, produce highly mobile carriers. With this understanding, we are able to achieve conductivities in this class of materials exceeding 20 S/cm.
关键词： semiconducting polymers,conductivity,ellipsometric porosimetry,GIWAXS,solution sequential processing,valence band level,F4TCNQ,poly(3-heptylselenophene),AC Hall effect,poly(3-hexylthiophene),DSC,bandgap,chemical doping,crystallinity
更新于2025-09-04 15:30:14
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Anisotropic conductivity of Cellulose-PEDOT:PSS composite materials studied with a generic 3D four-point probe tool
摘要： The conductive polymer poly(3,4-ethylenedioxythiphene):poly(styrenesulfonate) (PEDOT:PSS) is widely used in organic electronics and printed electronics due to its excellent electronic and ionic conductivity. PEDOT:PSS films exhibit anisotropic conductivities originating from the interplay of film deposition processes and chemical structure. The previous studies found that high boiling point solvent treated PEDOT:PSS exhibits an anisotropy of 3 to 4 orders magnitude. Even though both the in-plane and out-of-plane conductivities are important for the device performance, the out-of-plane conductivity is rarely studied due to the complexity with the experiment procedure. Cellulose-based paper or films can also exhibit anisotropic behavior due to the combination of their intrinsic fibric structure and film formation process. We have previously developed a conductive paper based on PEDOT:PSS and cellulose which could be used as the electrodes in energy storage devices. In this work we developed a novel measurement set-up for studying the anisotropy of the charge transport in such composite materials. A tool with two parallel plates mounted with spring loaded probes was constructed enabling probing both lateral and vertical directions and resistances from in-plane and out-of-plane directions to be obtained. The measurement results were then input and analyzed with a model based on a transformation method developed by Montgomery, and thus the in-plane and out-of-plane conductivities could be detangled and derived. We also investigated how the conductivity anisotropy depends on the microstructure of the cellulose template onto which the conductive polymer self-organizes. We show that there is a relatively small difference between the in-plane and out-of-plane conductivities which is attributed to the unique 3D-structure of the composites. This new knowledge gives a better understanding of the possibilities and limitations for using the material in electronic and electrochemical devices.
关键词： Cellulose,PEDOT:PSS,composite material,anisotropic conductivity,four-point probe
更新于2025-09-04 15:30:14
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Surfaces of axion insulators
摘要： Axion insulators are magnetic topological insulators in which the nontrivial Z2 index is protected by inversion symmetry instead of time-reversal symmetry. The naturally gapped surfaces of axion insulators give rise to a half-quantized surface anomalous Hall conductivity (AHC), but the sign of the surface AHC cannot be determined from topological arguments. In this paper, we consider topological phenomena at the surface of an axion insulator. To be explicit, we construct a minimal tight-binding model on the pyrochlore lattice and investigate the all-in-all-out (AIAO) and ferromagnetic (FM) spin configurations. We also implement a recently proposed approach for calculating the surface AHC directly, which allows us to explore how the interplay between surface termination and magnetic ordering determines the sign of the half-quantized surface AHC. In the case of AIAO ordering, we show that it is possible to construct a topological state with no protected metallic states on boundaries of any dimension (surfaces, hinges, or corners), although chiral hinge modes do occur for many surface configurations. In the FM case, rotation of the magnetization by an external field offers promising means of control of chiral hinge modes, which can also appear on surface steps or where bulk domain walls emerge at the surface.
关键词： pyrochlore lattice,all-in-all-out,topological insulators,axion insulators,ferromagnetic,anomalous Hall conductivity
更新于2025-09-04 15:30:14
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High energy shift in the optical conductivity spectrum of the bilayer graphene
摘要： We calculate theoretically the optical conductivity in the bilayer graphene by considering Kubo-Green-Matsubara formalism. Different regimes of the interlayer coupling parameter have been considered in the paper. We show that the excitonic effects substantially affect the optical conductivity spectrum at the high-frequency regime when considering the full interaction bandwidth, leading to a total suppression of the usual Drude intraband optical transition channels and by creating a new type of optical gap. We discuss the role of the interlayer coupling parameter and the Fermi level on the conductivity spectrum, going far beyond the usual tight-binding approximation scheme for the extrinsic bilayer graphene.
关键词： interlayer coupling,excitonic effects,Kubo-Green-Matsubara formalism,bilayer graphene,optical conductivity
更新于2025-09-04 15:30:14
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AC Conductivity and Dielectric Properties of (1? <i>x</i> )(0.94Bi <sub/>0.5</sub> Na <sub/>0.5</sub> TiO <sub/>3</sub> –0.06BaTiO <sub/>3</sub> )– <i>x</i> Ta Lead Free Ceramics
摘要： Piezoelectric ceramics such as Pb(Zr,Ti)O3 (PZT) are currently used by electronic devices because of their superb properties. Lead-based ceramics has caused a lot of environmental problems due to their toxicity. So, lead-free ceramics have been studied as an alternative method due to the toxicity of lead-based ceramics. Lead-free energy harvesting application (Bi0.5Na0.5TiO3–BaTiO3 (BNT-BT), is famous for its excellent piezoelectric and electrical properties. The substitution of BNT-BT and Ta5+ also is very effective in improving the relative dielectric permittivity and electrical properties. Because of the device performance depends on the relative dielectric permittivity, temperature and frequency of ceramic are very important condition. In this study, the electrical and relative dielectric permittivity of substitution of BNT-BT with Ta will be analyzed and AC conductivity depending on temperature and frequency will be shown. Also, it will calculate and analyze activation energy in different ranges of frequency.
关键词： BNT-BT,AC Conductivity
更新于2025-09-04 15:30:14
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Atomistic Insight into Ion Transport and Conductivity in Ga/Al-Substituted Li <sub/>7</sub> La <sub/>3</sub> Zr <sub/>2</sub> O <sub/>12</sub> Solid Electrolytes
摘要： Garnet-structured Li7La3Zr2O12 is a promising solid electrolyte for next-generation solid-state Li batteries. However, sufficiently fast Li-ion mobility required for battery applications only emerges at high temperatures, upon a phase transition to cubic structure. A well-known strategy to stabilize the cubic phase at room temperature relies on aliovalent substitution; in particular, the substitution of Li+ by Al3+ and Ga3+ ions. Yet, despite having the same formal charge, Ga3+ substitution yields higher conductivities (10?3 S/cm) than Al3+ (10?4 S/cm). The reason of such difference in ionic conductivity remains a mystery. Here we use molecular dynamic simulations and advanced sampling techniques to precisely unveil the atomistic origin of this phenomenon. Our results show that Li+ vacancies generated by Al3+ and Ga3+ substitution remain adjacent to Ga3+ and Al3+ ions, without contributing to the promotion of Li+ mobility. However, while Ga3+ ions tend to allow limited Li+ diffusion within their immediate surroundings, the less repulsive interactions associated with Al3+ ions lead to a complete blockage of neighboring Li+ diffusion paths. This effect is magnified at lower temperatures, and explains the higher conductivities observed for Ga-substituted systems. Overall this study provides a valuable insight into the fundamental ion transport mechanism in the bulk of Ga/Al-substituted Li7La3Zr2O12 and paves the way for rationalizing aliovalent substitution design strategies for enhancing ionic transport in these materials.
关键词： Li-ion conductivity/diffusion,enhanced sampling hybrid Monte Carlo,Molecular Dynamics,GSHMC,Ga/Al-substituted LLZO,Solid electrolytes
更新于2025-09-04 15:30:14