Evidence for Anomalous Bond Softening and Disorder Below 2 nm Diameter in Carbon-Supported Platinum Nanoparticles from the Temperature-Dependent Peak Width of the Atomic Pair Distribution Function

X-ray pair distribution function (PDF) analysis has been applied to five carbon-supported platinum nanoparticles with sizes ranging from 1.78(2) to 11.2(2) nm. Debye (θ_D) and Einstein (θ_E) temperatures were extracted from temperature-dependent PDF peak widths. A monotonic decrease in (θ_D) with nanoparticle diameter was found and could be well explained by the effect of increased surface area except in the case of the 1.78(2) nm diameter nanoparticle where the measured Debye temperature is significantly depressed from that predicted. This suggests an anomalous bond softening in the smallest sample

Tailoring the Seebeck Coefficient of PEDOT:PSS by Controlling Ion Stoichiometry in Ionic Liquid Additives

Mixing simple additives into poly­(3,4-ethylenedioxythiophene)/poly­(styrenesulfonate) (PEDOT:PSS) dispersions can greatly enhance the thermoelectric properties of the cast films with little manufacturing cost, but design rules for many of these additives have yet to emerge. We show that controlling stoichiometry in ionic liquid (I.L.) additives can decouple morphological and electronic modifications to PEDOT:PSS and enhance its power factor by over 2 orders of magnitude. Blending I.L. additives with a 1:1 stoichiometry between cationic imidazolium (Im⁺) derivatives and anionic bis­(trifluoromethane)­sulfonamide (TFSI^–) groups into PEDOT:PSS dispersions raised the film conductivity to ∼1000 S/cm. The Seebeck coefficient, which gives insight into the electronic structure as well as thermoelectric performance, remained unchanged. This behavior mimics that of popular high-boiling solvent additives such as dimethyl sulfoxide and ethylene glycol, which restructure the film morphology to enhance carrier mobility. Blending I.L. additives with a 4:1 stoichiometry between Im⁺ and TFSI^– groups raises the conductivity in a similar manner but also enhances the Seebeck coefficient. This selective Seebeck enhancement proceeds from the interaction of excess Im⁺ with anionic poly­(styrenesulfonate) (PSS^–) groups, similar to previous studies using inorganic salts, that results in a shift in charge carrier populations. Inorganic salts by themselves cannot raise the conductivity of PEDOT:PSS to appropriate values since they lack the solvent restructuring effect. These I.L. additives combine the effects of high-boiling solvents and diffuse ions, with the ability to tailor the Seebeck coefficient through ion stoichiometry

Electrochemistry of DNA Monolayers Modified With a Perylenediimide Base Surrogate

Electrochemistry of self-assembled DNA monolayers represents an attractive strategy for understanding the intrinsic properties of DNA and for developing DNA-based sensors. Thus, there is much interest in the discovery and characterization of new redox-active probes for application in DNA-based technologies. Herein, we report a detailed study of the electrochemical properties of a perylene-3,4,9,10-tetracarboxylic diimide base surrogate, when incorporated at various positions within a DNA monolayer. We demonstrate that the redox chemistry of this perylenediimide probe is mediated by the DNA base pair stack, dependent on its location within the DNA monolayer, and activated thermally. The electrochemical features and general synthetic flexibility of the perylenediimide base surrogate appear favorable for assays that leverage DNA-mediated charge transport