3 research outputs found
Influence of Stacking Morphology and Edge Nitrogen Doping on the Dielectric Performance of Graphene–Polymer Nanocomposites
We demonstrate that functional groups
obtained by varying the preparation
route of reduced graphene oxide (rGO) highly influence filler morphology
and the overall dielectric performance of rGO-relaxor ferroelectric
polymer nanocomposite. Specifically, we show that nitrogen-doping
by hydrazine along the edges of reduced graphene oxide embedded in
polyÂ(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) results
in a dielectric permittivity above 10 000 while maintaining
a dielectric loss below 2. This is one of the best-reported dielectric
constant/dielectric loss performance values. In contrast, rGO produced
by the hydrothermal reduction route shows a much lower enhancement,
reaching a maximum dielectric permittivity of 900. Furthermore, functional
derivatives present in rGO are found to strongly affect the quality
of dispersion and the resultant percolation threshold at low loading
levels. However, high leakage
currents and lowered breakdown voltages offset the advantages of increased
capacitance in these ultrahigh-k systems, resulting in no significant
improvement in stored energy density
Metal-Free, Single-Polymer Device Exhibits Resistive Memory Effect
All-polymer, write-once-read-many times resistive memory devices have been fabricated on flexible substrates using a single polymer, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). Spin-cast or inkjet-printed films of solvent-modified PEDOT:PSS are used as electrodes, while the unmodified or as-is PEDOT:PSS is used as the semiconducting active layer. The all-polymer devices exhibit an irreversible but stable transition from a low resistance state (ON) to a high resistance state (OFF) at low voltages caused by an electric-field-induced morphological rearrangement of PEDOT and PSS at the electrode interface. However, in the metal–PEDOT:PSS–metal devices, we have shown a metal filament formation switching the device from an initial high resistance state (OFF) to the low resistance state (ON). The all-PEDOT:PSS memory device has low write voltages (<3 V), high ON/OFF ratio (>10<sup>3</sup>), good retention characteristics (>10 000 s), and stability in ambient storage (>3 months)
Solvent Vapor Annealing in the Molecular Regime Drastically Improves Carrier Transport in Small-Molecule Thin-Film Transistors
We demonstrate a new way to investigate and control the
solvent vapor annealing of solution-cast organic semiconductor thin
films. Solvent vapor annealing of spin-cast films of 6,13-bisÂ(triisopropylsilylethynyl)
pentacene (TIPS-Pn) is investigated in situ using quartz crystal microbalance
with dissipation (QCM-D) capability, allowing us to monitor both solvent
mass uptake and changes in the mechanical rigidity of the film. Using
time-resolved grazing incidence wide angle X-ray scattering (GIWAXS)
and complementary static atomic force microscopy (AFM), we demonstrate
that solvent vapor annealing in the molecular regime can cause significant
performance improvements in organic thin film transistors (OTFTs),
whereas allowing the solvent to percolate and form a liquid phase
results in catastrophic reorganization and dewetting of the film,
making the process counterproductive. Using these lessons we devise
processing conditions which prevent percolation of the adsorbed solvent
vapor molecules for extended periods, thus extending the benefits
of solvent vapor annealing and improving carrier mobility by nearly
two orders of magnitude. Ultimately, it is demonstrated that QCM-D
is a very powerful sensor of the state of the adsorbed solvent as
well as the thin film, thus making it suitable for process development
as well as in-line process monitoring both in laboratory and in future
manufacturing settings