The highest possible resolution for printed colour images is determined by the diffraction limit of visible light. To achieve this limit, individual colour elements (or pixels) with a pitch of 250 nm are required, translating into printed images at a resolution of ∼100,000 dots per inch (d.p.i.). However, methods for dispensing multiple colourants or fabricating structural colour through plasmonic structures have insufficient resolution and limited scalability. Here, we present a non-colourant method that achieves bright-field colour prints with resolutions up to the optical diffraction limit. Colour information is encoded in the dimensional parameters of metal nanostructures, so that tuning their plasmon resonance determines the colours of the individual pixels. Our colour-mapping strategy produces images with both sharp colour changes and fine tonal variations, is amenable to large-volume colour printing via nanoimprint lithography, and could be useful in making microimages for security, steganography, nanoscale optical filters and high-density spectrally encoded optical data storage.
The exact role of
a defect structure on transition metal compounds
for electrocatalytic oxygen evolution reaction (OER), which is a very
dynamic process, remains unclear. Studying the structure–activity
relationship of defective electrocatalysts under operando conditions is crucial for understanding their intrinsic reaction
mechanism and dynamic behavior of defect sites. Co3O4 with rich oxygen vacancy (VO) has been reported
to efficiently catalyze OER. Herein, we constructed pure spinel Co3O4 and VO-rich Co3O4 as catalyst models to study the defect mechanism and investigate
the dynamic behavior of defect sites during the electrocatalytic OER
process by various operando characterizations. Operando electrochemical impedance spectroscopy (EIS) and
cyclic voltammetry (CV) implied that the VO could facilitate
the pre-oxidation of the low-valence Co (Co2+, part of
which was induced by the VO to balance the charge) at a
relatively lower applied potential. This observation confirmed that
the VO could initialize the surface reconstruction of VO–Co3O4 prior to the occurrence
of the OER process. The quasi-operando X-ray photoelectron
spectroscopy (XPS) and operando X-ray absorption
fine structure (XAFS) results further demonstrated the oxygen vacancies
were filled with OH• first for VO–Co3O4 and facilitated pre-oxidation of low-valence
Co and promoted reconstruction/deprotonation of intermediate Co–OOH•. This work provides insight into the defect mechanism
in Co3O4 for OER in a dynamic way by observing
the surface dynamic evolution process of defective electrocatalysts
and identifying the real active sites during the electrocatalysis
process. The current finding would motivate the community to focus
more on the dynamic behavior of defect electrocatalysts.
MOF-derived ZnO@ZnO Quantum Dots/C core-shell nanorod arrays grown on flexible carbon cloth are successfully fabricated as a binder-free anode for Li-ion storage. In combination with the advantages from the ZnO/C core-shell architecture and the 3D nanorod arrays, this material satisfies both efficient ion and fast electron transport, and thus shows superior rate capability and excellent cycling stability.
High-resolution multicolor printing based on pixelated optical nanostructures is of great importance for promoting advances in color display science. So far, most of the work in this field has been focused on achieving static colors, limiting many potential applications. This inevitably calls for the development of dynamic color displays with advanced and innovative functionalities. In this Letter, we demonstrate a novel dynamic color printing scheme using magnesium-based pixelated Fabry-Pérot cavities by gray scale nanolithography. With controlled hydrogenation and dehydrogenation, magnesium undergoes unique metal and dielectric transitions, enabling distinct blank and color states from the pixelated Fabry-Pérot resonators. Following such a scheme, we first demonstrate dynamic Ishihara plates, in which the encrypted images can only be read out using hydrogen as information decoding key. We also demonstrate a new type of dynamic color generation, which enables fascinating transformations between black/white printing and color printing with fine tonal tuning. Our work will find wide-ranging applications in full-color printing and displays, colorimetric sensing, information encryption and anticounterfeiting.
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