Hysteresis and charge trapping in graphene quantum dots

We report current hysteresis in response to applied voltage in graphene quantum dots of average diameter 4.5±0.55 nm, synthesized electrochemically using multiwalled carbon nanotubes. In response to step voltages, transient current decay characteristic of deep and shallow level charge traps with time constants 186 ms and 6 s is observed. Discharging current transients indicate charge storage of the order of 100 µC. Trap states are believed to arise due to the fast physisorption of external adsorbates,which are found to havea significant effect on charge transport and changes the resistance of the prepared device by an order of 3

Spirothiopyran-Based Reversibly Saturable Photoresist

Super-resolution lithography holds the promise of achieving three-dimensional (3D) nanopatterning at deep subwavelength resolutions with high throughput. 3D super-resolution lithography schemes demonstrated thus far have all been serial in nature, primarily due to the lack of a photoresist chemistry that not only couples a saturable reversibly switchable reaction with a writing step but also has a low saturation threshold. Here, we demonstrate that combining the reversible photoisomerization of spirothiopyran with the thiol-Michael conjugate addition reaction achieves the necessary photochemical characteristics. Green light was found to saturate inhibition of the thiol-Michael addition writing step at very low intensity thresholds. By formulating a spirothiopyran-functionalized polyethylene glycol copolymer, we demonstrate spatial control over cross-linking using inhibition by green light. Kinetics measurements combined with photokinetic simulations show that interference lithography on a spirothiopyran maleimide-based writing system using conventional light sources (e.g., a 2 W green laser) should deliver super-resolution features (∼45 nm wide lines) in thick films (tens of microns) over large areas (hundreds of microns on a side). The unique combination of reversible photochromic switching of spirothiopyran with the thiol-Michael addition reaction marks an important step toward realizing a highly parallelized 3D super-resolution writing system

Switchable Full-Color Reflective Photonic Ellipsoidal Particles

Full-color reflective photonic ellipsoidal polymer particles, capable of a dynamic color change, are created from dendronized brush block copolymers (den-BBCPs) self-assembled by solvent-evaporation from an emulsion. Surfactants composed of dendritic monomer units allow for the precise modulation of the interfacial properties of den-BBCP particles to transition in shape from spheres to striped ellipsoids. Strong steric repulsions between wedge-type monomers promote rapid self-assembly of polymers into large domains (i.e., 153 nm <= D <= 298 nm). Of note, highly ordered axially stacked lamellae (i.e., number of layers >100) within an ellipsoid give rise to a near-perfect photonic multilayer. The reflecting color is readily tunable across the entire visible spectrum by alteration of the molecular weight from 477 to 1144 kDa. Finally, the photonic ellipsoids are functionalized with magnetic nanoparticles organized into bands on the particle surface to produce real-time on/off coloration by magnetic field-assisted activation. In total, the reported photonic ellipsoidal particles represent a new class of switchable photonic materials

Dynamic Coloration of Complex Emulsions by Localization of Gold Rings Near the Triphase Junction

Multiphase microscale emulsions are a material platform that can be tuned and dynamically configured by a variety of chemical and physical phenomena, rendering them inexpensive and broadly programmable optical transducers. Interface engineering underpins many of these sensing schemes but typically focuses on manipulating a single interface, while engineering of the multiphase junctions of complex emulsions remains underexplored. Herein, multiphilic triblock copolymer surfactants are synthesized and assembled at the triphase junction of a dynamically reconfigurable biphasic emulsion. Tailoring the linear structure and composition of the polymer surfactants provides affinity to each phase of the complex emulsion (hydrocarbon, fluorocarbon, and continuous water phase), yielding selective localization of polymers around the triphase junction. Conjugation of these polymers with gold nanoparticles, forming structured rings, affords a dynamic reflected isotropic structural color that tracks with emulsion morphology, demonstrating the uniquely enabling nature of a functionalized triphase interface. This color is the result of interference of light along the internal hydrocarbon/fluorocarbon interface, with the gold nanoparticles scattering and redirecting light into total internal reflection competent paths. Thus, the functionalization of the triphase junction renders complex emulsions colorimetric sensors, a powerful tool toward sensitive and simple sensing platforms