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Hybrid and pristine polyalkylthiophene Langmuir-Schaefer films: Relationships of electrical impedance spectroscopy measurements, barrier properties and polymer nanostructure
摘要： Molecular organization in solid state plays a central role on organic devices performance. In this sense, a thorough investigation of thin films with application in organic electronics is imperative. This work addressed the fabrication and the morphological, optical and electrical characterization of Langmuir-Schaefer (LS) films of poly(3-hexylthiophene) (P3HT), pristine and mixed with stearic acid (SA), and their use as the active layer in organic Schottky diodes. The floating materials isotherms showed the SA molecules acting as a stabilizer for the P3HT in the Langmuir trough. Moreover, deposited P3HT:SA films present significant morphological changes, an improvement of the films overall structural ordering and a more effective charge transport within the active layer through electrical outcome. The alternating current measurements along with theoretical fitting, using equivalent electrical circuits, provided a good alternative to investigate the interfacial effects of the P3HT and P3HT:SA films deposited onto Al and Au electrodes.
关键词： Electrical impedance spectroscopy,Structure-property relations,Polythiophene,Langmuir-Schaefer,Thin films
更新于2025-09-09 09:28:46
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Child-Langmuir law for photoinjectors
摘要： The space-charge ?eld at the cathode limits the current density extracted from particle sources such as photoinjectors. For a long time, the maximum current has been estimated by using the classical Child-Langmuir law, which is derived with an assumption inconsistent with the conditions of modern laser-driven electron guns. Here, we introduce a theoretical model that accurately accounts for space-charge effects in transversely con?ned particle beams emerging from photocathodes. The model enables us to (i) determine the maximum current density extractable from the photocathode for an arbitrary cathode radius, (ii) reveal its dependence on the transverse pro?le of the particle beam, and (iii) predict its upper limit for structured beams such as the ones produced by surface-plasmon resonance-enhanced photocathodes.
关键词： photocathodes,space-charge effects,Child-Langmuir law,photoinjectors,surface-plasmon resonance
更新于2025-09-09 09:28:46
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Photoelectrochemically Active N‐Adsorbing Ultrathin TiO <sub/>2</sub> Layers for Water‐Splitting Applications Prepared by Pyrolysis of Oleic Acid on Iron Oxide Nanoparticle Surfaces under Nitrogen Environment
摘要： Highly performing photocatalytic surfaces are nowadays highly desirable in energy fields, mainly due to their applicability as photo water-splitting electrodes. One of the current challenges in this field is the production of highly controllable and efficient photoactive surfaces on many substrates. Atomic layer deposition has allowed the deposition of photoactive TiO2 layers over wide range of materials and surfaces. However, nitrogen doping of the growing layers, a highly effective way of controlling the absorption edges of photoactive surfaced, is still a challenging task. Here, the preparation of hierarchical nanostructured surfaces based on Langmuir–Schaefer and atomic layer deposition is proposed. Ultrathin TiO2 layers that are photoelectrochemically active in water splitting are prepared by a relatively low-temperature catalytic decomposition of oleic acid capping layers of iron oxide nanoparticles and the posterior nitrogen adsorption. The results evidence that simple N-adsorption is sufficient to narrow the bandgap of TiO2 layers that is equal to bandgap narrowing (0.12 eV) observed for substitutionally N-doped materials. The photocatalytic activity tests of the prepared surfaces in water-splitting applications demonstrate ≈90% increase in the activity of the N-adsorbing TiO2 layers.
关键词： Langmuir–Schaefer,magnetite (Fe3O4),photocatalysis,titanium dioxide (TiO2),atomic layer deposition (ALD)
更新于2025-09-04 15:30:14
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Photodegradable coumarin-derived amphiphilic dendrons for DNA binding: Self-assembly and phototriggered disassembly in water and air-water interface
摘要： In this article, we demonstrate the self-assembly and photoresponive behavior of a novel coumarin-based amphiphilic dendron in both aqueous solution and air-water interface. The dendritic structure, namely C-IG1, was composed of a lipophilic cholesterol and hydrophilic poly(amido amine) (PAMAM) dendron, and the amphiphilic counterpart is interconnected by a photolabile coumarin carbonate ester, enabling the photoinduced degradation of the amphiphiles in protic solvents via SN1-like mechanism. A Nile red solubilization fluorescence assay suggests a low critical aggregation concentration for the micelle formation of C-IG1 in aqueous solutions (3.9 × 10?5 M); the Langmuir analysis further indicates that C-IG1 possesses significant compressibility in air-water interface, eventually forming homogeneous monolayers with a final molecular area (A0) of 36 ?2. Notably, the micelles and Langmuir monolayer are quite stable until photo-triggered dissociation based on the photodeavage of C-IG1 amphiphile activated by 365-nm incident light. Moreover, the transition in interfacial morphology of the Langmuir monolayer during the assembly and photodegradation processes also can be visually analyzed by incorporating Nile red probes with in situ monitoring through fluorescence microscopy. The thin film deposited on a glass substrate by the Langmuir-Blodgett technique also shows a photoresponsive behavior based on the change in the contact angles of a water droplet on the surface upon light stimulation. The binding affinity of C-IG1 and cyclic DNA determined by the fluorescence quenching analysis of the coumarin reporter suggests a ground-state macromolecular complexation process occurring through polyvalent interactions between the pseudodendrimers and biomacromolecules. The ethidium bromide displacement assay further indicates thus dendriplex formation at low nitrogen-to-phosphorous value (N/P < 1) and confirms that the decomplexation accompanied by DNA release can be achieved through an active phototriggered route under spatiotemporal control.
关键词： Dendrimers,Langmuir analysis,Photocleavage,Gene delivery,Amphiphilic dendrons
更新于2025-09-04 15:30:14
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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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H2S and NH3 Detection with Langmuir-Schaefer Monolayer Organic Field-Effect Transistors
摘要： In this work gas sensing properties of Langmuir-Schaefer monolayer organic field-effect transistors (LS OFETs) prepared from organosilicon derivative of [1]benzothieno[3,2-b][1]-benzothiophene (BTBT) have been investigated. The monolayer has been deposited using Langmuir-Schaefer method, which results in a uniform low-defect monolayer with excellent electrical performance, hole mobility up to 7 × 10?2 cm2 V?1 s?1, the threshold voltage around 0 V and on-off ratio of 104. Developed sensors demonstrate a long-term stability of a half-year storage under ambient conditions. Preliminary investigations demonstrated that the LS OFETs give instantaneous response on ammonia and hydrogen sulfide at low concentrations. The results reported open new perspectives for the OFET-based gas-sensing technology.
关键词： OFETs,monolayer,organic electronics,chemical sensing,Langmuir-Schaefer
更新于2025-09-04 15:30:14
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Langmuir–Hinshelwood and Light-Intensity Dependence Analyses of Photocatalytic Oxidation Rates by Two-Dimensional-Ladder Kinetic Simulation
摘要： Though photocatalytic reactions gather enormous attention, dependences of light intensity and reactant concentration have not been concurrently expressed clearly. In the previously reported studies, a quadratic formula equation obtained from the conventional analysis using the concentration of electron?hole pairs has been modified. In this report we numerically simulated the reaction with a two-dimensional(2D)-ladder kinetics without using electron?hole concentrations. In fundamental processes, (i) photoabsorption, (ii) reduction, (iii) oxidation, and (iv) recombination, were treated as the transitions between the states of each powder characterized by the numbers of possessing negative and positive charges. Through the numerical 2D-ladder simulation with various rate constants, the light-intensity (I) dependence of the oxidation rate was found to be fully expressed by involving the square of the intrinsic quantum yield into the square root part of the well-known quadratic formula equation. The square root dependence of the reaction rate, r ∝ I1/2, could be expected only when the rate of the reduction is extremely smaller than the recombination rate at the normal light intensity. Then, the resultant equations obtained with this 2D-ladder simulation were transformed to the equation for Langmuir?Hinshelwood kinetics with two parameters, rL and KL, which correspond to the intrinsic oxidation rate and the adsorption equilibrium constant of the reactant, respectively. Light-intensity dependence of KL was expressed by adding two terms proportional to I2 to both the adsorption and desorption rate constants. The reported experimental data sets of the decomposition rates for phenol and 4-chlorophenol were fitted with the proposed equation, and then from the obtained parameter values the formation rate of (cid:129)O2? could be estimated and found to be compatible to that which has been experimentally measured. Thus, the present analytical treatment is actually the simple and useful method to understand the dependencies of reactant concentration and light-intensity on the photocatalytic oxidation rates.
关键词： reactant concentration,photocatalytic reactions,light intensity,Langmuir?Hinshelwood kinetics,two-dimensional-ladder kinetics
更新于2025-09-04 15:30:14
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Simulations of the generation of energetic electrons and the formation of descending artificial plasma layers during HF‐heating at Arecibo
摘要： HF-induced Descending Artificial Plasma Layers (DAPLs) are artificially ionized plasma layers with plasma density in excess of that of the F2-peak. They were discovered during HF heating experiments at HAARP where they descended up to 70 km from the initial O mode wave reflection height. The DAPLs were attributed to the ionization of the neutral gas by high-energy electrons accelerated by the artificial ionospheric turbulence. Recently, DAPL formation was reported during the HF-heating experiment at Arecibo [Bernhardt et al., 2017]. This result was unexpected since Arecibo has the Effective Radiated Power (ERP) 4 – 5 times lower than that at HAARP, and since the experiment at Arecibo also has an unfavorable geometry, where the HF beam is directed vertically while the inclination of the geomagnetic field is 43.5o, allowing the fast electrons to escape the volume where their interaction with the artificial plasma turbulence occurs. However, the presence of photoelectrons due to the UV radiation from the Sun at the low latitude of Arecibo could magnify the flux of hot electrons. A model of artificial plasma layers created by the Arecibo HF facility is presented. It shows that Langmuir turbulence due to the HF heating can accelerate part of the ambient photoelectrons to energies above the ionization threshold of the neutral gas, leading to the formation of DAPLs. The present model results are in quantitative agreement with the experiments of Bernhardt et al. [2017].
关键词： HAARP,HF heating experiments,photoelectrons,HF-induced Descending Artificial Plasma Layers,Arecibo,Langmuir turbulence,DAPLs
更新于2025-09-04 15:30:14