We cross-correlate the hydration-dependent structure and properties – microscopic and macroscopic – of a thin Nafion ionomer film on an electrochemically pertinent Pt substrate.
A tunable topology and a porous network make π-conjugated covalent organic frameworks (COFs) a new class of organic semiconductors for optoelectronic, smart sensing, and catalytic applications. Although some of the COFs exhibit enhanced electric conductivity with a high charge carrier mobility, the nature and pathways of charge transport still remain elusive. In order to unveil the transport mechanism, herein, we have developed crystalline π-conjugated COFs using planar building blocks, and a wafer-scale self-supporting thin film was grown, which could be transferred onto any of the desired substrates. The COF film was found to be highly oriented and exhibited a high in-plane electronic conductivity. The conductivity was almost independent of temperature with an ultra-low activation energy of 14.3 meV, approaching a band-like transport of charge carriers within the crystalline domains. The COF films also showed a high photoresponsivity in electronic conduction against a complete visible range, demonstrated as a flexible photodetector device. This work represents a thorough investigation of the mechanism and direction of charge transport in crystalline π-conjugated COF semiconductors, which suggests their feasibility as key active materials in multi-functional organic electronics.
We proposed and demonstrated a simple but deterministic scheme for generating polarization-entangled photon pairs at telecommunication wavelengths with type-II quasi-phase-matched spontaneous parametric down-conversion (QPM-SPDC) having two poling periods. We fabricated a LiNbO3 crystal having two poling periods so as to generate entangled photons at two wavelengths, i.e., 1506 nm and 1594 nm. We characterized the two-photon polarization state with state tomography and confirmed that the state was highly entangled.
The surface effects and anchoring of liquid crystals (LCs) have long been significant concerns for material chemists and physicists.[1] The surface alignment of LCs by mechanical rubbing [2] is a widely recognized phenomenon and of particular significance in technological applications for display device fabrication.[3] Surface molecular orientations [4] and topographical grooves and undulations [5] of the substrate provide LC alignment effects. Furthermore, in the past two decades, the photoalignment of LCs on photoreactive polymer film surfaces by anisotropic irradiation [6] has become a significant method and an alternative to mechanical rubbing processes. The aligning substrates are not limited to polymer surfaces; various types of surfaces, such as hard inorganic materials [7] and soft bio-related interfaces, [8] can be used for the alignment induction. In addition to low-molecular-mass LCs, polymer LC materials are also aligned by the surface effect.[9] Despite the tremendous amount of accumulated knowledge and the number of potential applications, the surface alignment processes developed to date mostly involve manipulations on the surfaces of solid or condensed phases.Herein, we report on LC alignment alternation, which is attained by a modification of the free surface (air-film interface). The homeotropic surface anchoring effect and layer structuring at the free surface of calamitic LC molecules have been shown experimentally [10] and have been further verified by theoretical simulations.[11] To modify the free surface, the present approach adopts the surface segregation [12,13] of a small amount of a free-surface-active polymer. We demonstrate here that the coverage of the surface with the free-surface-active polymer leads to a homeotropic-to-parallel orientation change of LC mesogens, which further leads to an efficient in-plane photoalignment of microphase separation (MPS) domains of a relevant LC block copolymer by linearly polarized light (LPL).[14] With regard to the MPS alignment control, the important role of a top coat layer has recently been demonstrated by Bates et al. [15] In this case, a polar-to-nonpolar chemical conversion of the top layer is achieved to fulfill the requirement of spin-casting from an aqueous solvent and to provide a neutral (non-preferential) layer for the hydrophobic block copolymer during the annealing. In the present approach, in contrast, no additional coating procedure is required, providing a simple, versatile method for the desired alignment control of MPS domains.First, the alignment behavior of an LC azobenzene (Az) homopolymer (PAz in Figure 1 a; M n = 8.0 10 4 , M w /M n = 1.13, and g-43 8C-SmC-100 8C-SmA-120 8C-iso) was examined. A spincast film of PAz was prepared (thickness: 100-200 nm) from a chloroform solution. After annealing at 130 8C (above the isotropization temperature) for 10 min followed by gradual cooling via a smectic LC phase to room temperature, this film spontaneously formed the out-of-plane (perpendicular) orientation of Az side mesogens, a...
Development of efficient and well-controlled nonclassical photon sources is one of the keys in the quantum information and communication technology. We present our recent activities to develop advanced sources of photon pairs having controlled frequency correlation, by use of quasi-phase matching (QPM) and extended phase-matching (EPM). First, we present the generation of polarization and frequency entangled photons using QPM having two poling periods. We also demonstrate the photon pair generation with controlled frequency correlation and its application to making heralded single photons with intrinsically pure spectrotemporal modes.
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