Chemical Vapor Deposition Synthesis of Tunable Unsubstituted Polythiophene

Despite having exceptional electroactive properties, applications of unsubstituted polythiophene (PTh) have been limited due to its insolubility. To overcome this challenge, we have employed oxidative chemical vapor deposition (oCVD) as a unique liquid-free technique to enable the oxidative polymerization of PTh using thiophene as the starting monomer and vanadium oxytrichloride as an effective vaporizable oxidant initiator. Vibrational and phototelectron spectroscopy indicated the formation of unsubstituted polythiophene. Cyclic voltammetry revealed its electrochromic behavior in solution. Significantly, polymer conjugation length and electrical conductivity can be tuned by controlling oCVD process variables. Polymerization is found to be adsorption-limited, so by providing sufficient monomer and limiting the amount of initiator at the growth surface, PTh is believed to be formed through α–α thiophene linkages

Influence of oCVD Polyaniline Film Chemistry in Carbon-Based Supercapacitors

Polyaniline (PANI) is integrated into Mo₂C carbide-derived-carbon (CDC) electrodes using the single-step, solvent-free process of oxidative chemical vapor deposition (oCVD). By optimizing the oCVD processing conditions, CDC electrodes integrated with oCVD PANI exhibit more than double the gravimetric capacitance (115 F/g) vs bare CDC electrodes (52 F/g) and a 79% capacity retention after over 10 000 cycles. The oxidant flow rate, substrate temperature, and reactor pressure were varied, and their influence on film chemistry and supercapacitor performance was explored electrochemically and with FTIR and XPS. The study reveals that a higher substrate temperature, pressure, and oxidant flow rate are critical for depositing emeraldine PANI for optimal electrochemical performance. Interestingly, the optimally performing PANI-CDC devices have a porous PANI morphology as determined by SEM, which may facilitate ion transport, improve scan rate performance, and impart electric double layer capacitance in addition to the intrinsic Faradaic pseudocapacitance

Enhanced Charge Storage of Ultrathin Polythiophene Films within Porous Nanostructures

In a single step polymerization and coating, oxidative chemical vapor deposition (oCVD) has been used to synthesize unsubstituted polythiophene. Coatings have been conformally coated within porous nanostructures of anodized aluminum oxide, titanium dioxide, and activated carbon. Significant enhancement in charge capacity has been found with ultrathin polythiophene coatings that preserve the surface area and pore space of the nanostructures. Pseudocapacitors consisting of ultrathin polythiophene coated within activated carbon yielded increases of 50 and 250% in specific and volumetric capacitance compared with bare activated carbon. Devices were stable up to the 5000 cycles tested with only a 10% decrease in capacitance

Thickness-Dependent Crossover from Charge- to Strain-Mediated Magnetoelectric Coupling in Ferromagnetic/Piezoelectric Oxide Heterostructures

Magnetoelectric oxide heterostructures are proposed active layers for spintronic memory and logic devices, where information is conveyed through spin transport in the solid state. Incomplete theories of the coupling between local strain, charge, and magnetic order have limited their deployment into new information and communication technologies. In this study, we report direct, local measurements of strain- and charge-mediated magnetization changes in the La_0.7Sr_0.3MnO₃/PbZr_0.2Ti_0.8O₃ system using spatially resolved characterization techniques in both real and reciprocal space. Polarized neutron reflectometry reveals a graded magnetization that results from both local structural distortions and interfacial screening of bound surface charge from the adjacent ferroelectric. Density functional theory calculations support the experimental observation that strain locally suppresses the magnetization through a change in the Mn-e_g orbital polarization. We suggest that this local coupling and magnetization suppression may be tuned by controlling the manganite and ferroelectric layer thicknesses, with direct implications for device applications